I'm showing you my current bookmarks toolbar, here... I feel so naked... the red arrow points to the Google Calendar favicon*.
Sometimes it's the little details that delight. That Calendar favicon used to only display "31". Which was perfect for what it was, a calendar icon.
Now they've updated it so the number on the Google Calendar favicon is what day it actually is! So today, on April 27, the favicon is a 27.
It's cute, yeah; but also, the icon is using its tiny patch of browser real estate to give you information.
*
"favicon" is the name of the tiny picture, or icon, that represents a website in browser tabs and bookmark lists. Bookmarks toolbars show these icons in folders, and also let you place just the favicon up, as a quick link to that site.