Wiki uses the favicon mechanism to label the origin in a browser tab. We call these flags and use them in many other circumstances. We generate them so that they are recognizable as distinct but still part of a family.
The algorithm picks a light and dark color and then generates a gradient between them. The gradient from light to dark goes from top to bottom with a random rotational gradient from -90 to +90 degrees. github 
The artistic vision was a landscape with sky over ground.
Our second server implementation placed dark over light. The effect is that of landscape at night. github
We call these Flags. They are not icons because they don't represent anything. Flags are used as backgrounds for fork actions. Gradients work for this. Pictures don't.
Think of this as branding for wiki and all it stands for like creative commons, open source, cross-origin resource sharing and powerful plugins. Not only this but we share the branding with each site that runs wiki. Be proud.