Square - If you have an account that isn’t linked to a verified bank account, you see a little pressure gauge icon giving a visual warning that the potential transaction is too high for an unverified account.
Adium- The eyes of the bird icon open while using Adium and close when you close the app.
/via Bartosz Hernas
Pixelmator - The “Open recent picture” on the start screen of Pixelmators displays the actual last opened picture right in the icon (see the image in between the brush and the wooden board).
Gnome - on the icon of .txt files, you can see a summary of first three rows for particular file.
/via Drazen Peric
Tumblr - New blog post menu features icons on strips of paper, which together form one long strip of paper.