This hook_world_alter() T-shirt idea was something Trevor Twining came up with way back at DrupalCon DC. I got a single T-shirt made for DrupalCon Paris. A number of people said they wanted one – though since I'm not interested in the business of making T-shirts, I thought I'd make the vector file available for anyone and everyone's use.
Enjoy!
This design is available under the Creative Commons Attribution-Share Alike license.