diff --git a/DESCRIPTION b/DESCRIPTION
index f9f75f1..75a3f84 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -30,6 +30,8 @@ Description: Query and print information about the current R
 License: GPL-2
 URL: https://github.com/r-lib/sessioninfo#readme
 BugReports: https://github.com/r-lib/sessioninfo/issues
+Depends: 
+    R (>= 2.10)
 Imports:
     cli,
     tools,
diff --git a/NAMESPACE b/NAMESPACE
index 971546d..225a4be 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -5,10 +5,12 @@ S3method(as.character,packages_info)
 S3method(as.character,platform_info)
 S3method(as.character,python_info)
 S3method(as.character,session_info)
+S3method(c,platform_info)
 S3method(format,external_info)
 S3method(format,packages_info)
 S3method(format,platform_info)
 S3method(format,python_info)
+S3method(format,session_info)
 S3method(print,external_info)
 S3method(print,packages_info)
 S3method(print,platform_info)
diff --git a/R/hash.R b/R/hash.R
new file mode 100644
index 0000000..ec81383
--- /dev/null
+++ b/R/hash.R
@@ -0,0 +1,43 @@
+
+# TODO: this can use cli, once a new version with cli::hash_emoji() is
+# release to CRAN
+
+add_hash <- function(si, size = 3) {
+  stopifnot(size >= 1, size <= 4)
+
+  orig <- si
+  # drop the date for hashing
+  if ("platform" %in% names(si) && "date" %in% names(si$platform)) {
+    si$platform$date <- NULL
+  }
+
+  old <- options(
+    cli.unicode = FALSE,
+    cli.num_colors = 1,
+    sessioninfo.emoji = FALSE
+  )
+  on.exit(options(old), add = TRUE)
+  tmp <- tempfile()
+  writeLines(format(si), tmp)
+  on.exit(unlink(tmp), add = TRUE)
+
+  md5 <- tools::md5sum(tmp)[[1]]
+  md513 <- substr(md5, 1, 13)
+  mdint <- as.integer(as.hexmode(strsplit(md513, "")[[1]]))
+  hash <- sum(mdint * 16^(0:12))
+
+  base <- nrow(emojis)
+  ehash <- hash %% (base ** size)
+  digits <- integer()
+  while (ehash > 0) {
+    digits <-  c(digits, ehash %% base)
+    ehash <- ehash %/% base
+  }
+  digits <- c(digits, rep(0, 10))[1:size]
+
+  nms <- emojis$name[digits + 1]
+  emo <- emojis$emoji[digits + 1]
+
+  orig$hash <- list(emoji = emo, emo_text = nms)
+  orig
+}
diff --git a/R/platform-info.R b/R/platform-info.R
index b59e6ff..dcc32e5 100644
--- a/R/platform-info.R
+++ b/R/platform-info.R
@@ -24,7 +24,7 @@
 #' platform_info()
 
 platform_info <- function() {
-  structure(drop_null(list(
+  as_platform_info(drop_null(list(
     version = R.version.string,
     os = os_name(),
     system = version$system,
@@ -36,7 +36,7 @@ platform_info <- function() {
     date = format(Sys.Date()),
     rstudio_version = get_rstudio_version(),
     pandoc_version = get_pandoc_version()
-  )), class = c("platform_info", "list"))
+  )))
 }
 
 get_rstudio_version <- function() {
@@ -98,3 +98,15 @@ print.platform_info <- function(x, ...) {
 as.character.platform_info <- function(x, ...) {
   format(x, ...)
 }
+
+#' @export
+
+c.platform_info <- function(...) {
+  as_platform_info(NextMethod())
+}
+
+as_platform_info <- function(x) {
+  stopifnot(is.list(x))
+  class(x) <- c("platform_info", "list")
+  x
+}
diff --git a/R/printing.R b/R/printing.R
index b7aae88..456431d 100644
--- a/R/printing.R
+++ b/R/printing.R
@@ -1,11 +1,11 @@
 
 #' @importFrom cli symbol
 
-rule <- function (..., pad = NULL) {
-  if (is.null(pad)) pad <- symbol$line
+rule <- function (..., pad = NULL, double = FALSE) {
+  if (is.null(pad)) pad <- if (double) symbol$double_line else symbol$line
   title <- if (length(list(...))) paste0(" ", ..., " ") else ""
 
-  width <- max(cli::console_width() - nchar(title) - 3, 0)
+  width <- max(cli::console_width() - cli::ansi_nchar(title, "width") - 3, 0)
   paste(pad, title, paste(rep(pad, width), collapse = ""), sep = "")
 }
 
diff --git a/R/session-info.R b/R/session-info.R
index e8df85f..9310a42 100644
--- a/R/session-info.R
+++ b/R/session-info.R
@@ -90,6 +90,8 @@ session_info <- function(
     class = c("session_info", "list")
   )
 
+  si <- add_hash(si)
+
   if (is_string(to_file)) {
     writeLines(as.character(si), to_file)
     invisible(si)
@@ -100,24 +102,67 @@ session_info <- function(
 
 #' @export
 
-as.character.session_info <- function(x, ...) {
-  c(if ("platform" %in% names(x)) {
-      c(rule("Session info"), as.character(x$platform), "")
+format.session_info <- function(x, ...) {
+
+  has_platform <- !is.null(x$platform)
+
+  c(if (!"platform" %in% names(x)) {
+      c(rule(paste("Session info", emo_hash(x)), double = TRUE), text_hash(x))
+    },
+    if ("platform" %in% names(x)) {
+      c(rule(paste("Session info", emo_hash(x))),
+        text_hash(x),
+        format(x$platform),
+        ""
+      )
     },
     if ("packages" %in% names(x)) {
-      c(rule("Packages"), as.character(x$packages), "")
+      c(rule("Packages"), format(x$packages), "")
     },
     if ("external" %in% names(x)) {
-      c(rule("External software"), as.character(x$external), "")
+      c(rule("External software"), format(x$external), "")
     },
     if ("python" %in% names(x)) {
-      c(rule("Python configuration"), as.character(x$python), "")
+      c(rule("Python configuration"), format(x$python), "")
     }
   )
 }
 
 #' @export
 
+as.character.session_info <- function(x, ...) {
+  format(x, ...)
+}
+
+has_emoji <- function () {
+  if (isTRUE(opt <- getOption("sessioninfo.emoji"))) {
+    TRUE
+  } else if (identical(opt, FALSE)) {
+    FALSE
+  } else if (!cli::is_utf8_output()) {
+    FALSE
+  } else {
+    Sys.info()[["sysname"]] == "Darwin"
+  }
+}
+
+emo_hash <- function(x) {
+  if (is.null(x$hash)) return("")
+  if (has_emoji()) {
+    paste0(" ", paste(x$hash$emoji, " ", collapse = ""))
+  } else {
+    ""
+  }
+}
+
+text_hash <- function(x) {
+  if (!is.null(x$hash) && !has_emoji()) {
+    c(paste0(" hash: ", paste(x$hash$emo_text, collapse = ", ")), "")
+  }
+}
+
+#' @export
+
 print.session_info <- function(x, ...) {
-  cat(as.character(x), sep = "\n")
+  cat(format(x), sep = "\n")
 }
diff --git a/R/sysdata.rda b/R/sysdata.rda
new file mode 100644
index 0000000..1a857d4
Binary files /dev/null and b/R/sysdata.rda differ
diff --git a/tools/bad-emoji.R b/tools/bad-emoji.R
new file mode 100644
index 0000000..deb2dbe
--- /dev/null
+++ b/tools/bad-emoji.R
@@ -0,0 +1,203 @@
+# emoji 0.2.0
+bad <- c(
+  11,
+  24,
+  33,
+  34,
+  37,
+  43:45,
+  50,
+  67,
+  71,
+  76,
+  86,
+  101,
+  144:147,
+  155,
+  157,
+  170,
+  209:232,
+  239:250,
+  264:269,
+  325:330,
+  379:384,
+  403:422,
+  454:455,
+  474:479,
+  487:488,
+  496,
+  545:568,
+  605:610,
+  617:622,
+  629:634,
+  641:670,
+  695:718,
+  725:748,
+  755:778,
+  785:808,
+  815:838,
+  845:898,
+  905:928,
+  935:958,
+  965:1000,
+  1025:1030,
+  1043:1048,
+  1061:1072,
+  seq(1074, 1096, by = 2),
+  1097:1102,
+  1115:1120,
+  1133:1138,
+  1151:1156,
+  1169:1174,
+  1187:1192,
+  1205:1210,
+  1223:1228,
+  1241:1246,
+  1259:1270,
+  seq(1272, 1294, by = 2),
+  1295:1300,
+  1313:1318,
+  1337,
+  1360,
+  1368:1395,
+  1402:1431,
+  1438:1467,
+  1486:1509,
+  1528:1551,
+  1558:1581,
+  1588:1599,
+  1606:1623,
+  1642:1647,
+  1654:1677,
+  1684:1707,
+  1714:1737,
+  1744:1767,
+  1774:1797,
+  1804:1827,
+  1834:1857,
+  1859:1862,
+  1864:1868,
+  1875:1898,
+  1905:1928,
+  1935:2072,
+  2079:2102,
+  2123:2126,
+  2133:2156,
+  2163:2186,
+  2209:2236,
+  2243:2521,
+  2528:2551,
+  2558:2581,
+  2588:2611,
+  2624:2649,
+  2652:2656,
+  2658:2662,
+  2664:2668,
+  2670:2674,
+  2678:2682,
+  2684:2688,
+  2690:2684,
+  2696:2700,
+  2704:2708,
+  2710:2714,
+  2716:2720,
+  2722:2726,
+  2729:2773,
+  2775:2825,
+  2827:2877,
+  2879:2929,
+  2931:2975,
+  2977:3027,
+  3029:3079,
+  3081:3131,
+  3162,
+  3176,
+  3179,
+  3180,
+  3187,
+  3197,
+  3214,
+  3225,
+  3229,
+  3230,
+  3233:3235,
+  3253:3255,
+  3270,
+  3277,
+  3283,
+  3286,
+  3293,
+  3294,
+  3299,
+  3309,
+  3322,
+  3323,
+  3338,
+  3341,
+  3350,
+  3354,
+  3355,
+  3358,
+  3363,
+  3367,
+  3380,
+  3382,
+  3387,
+  3391,
+  3415,
+  3433,
+  3444,
+  3446:3449,
+  3456,
+  3489,
+  3490,
+  3516,
+  3535,
+  3565,
+  3574:3576,
+  3580,
+  3589,
+  3596,
+  3613,
+  3678,
+  3778,
+  3784,
+  3785,
+  3788,
+  3790,
+  3798:3800,
+  3819:3821,
+  3827,
+  3837:3840,
+  3849,
+  3856,
+  3863,
+  3892,
+  3897,
+  3899,
+  3908,
+  3944,
+  3965,
+  4041,
+  4053,
+  4057,
+  4059,
+  4067,
+  4071,
+  4074,
+  4087:4089,
+  4092,
+  4093,
+  4098,
+  4100,
+  4103,
+  4104,
+  4110,
+  4112,
+  4113,
+  4120,
+  4124,
+  4125,
+  4399,
+  4436:4441
+)