Skyicons are small pixel-icons following specific rules.
For example, they can be used as placeholders for profile pictures.
Every Skyicon can be identified by its unique fingerprint which is a 9-digit hexadecimal number representing the 6x6 pixels.
DE4D8057F would look like this:
1 1 0 1 1 1 1 0 0 1 0 0 1 1 0 1 1 0 0 0 0 0 0 0 0 1 0 1 0 1 1 1 1 1 1 1