Satoshis T-Shirts
Description: 2.1E15 = 21,000,000 times 100,000,000, i.e. the maximum number of Satoshis that will ever exist. Sure, it's rounded, but close enough. This variation uses the scientific notation instead of loads of zeros, to make it a bit more cryptic.
Description: A reminder for Bitcoin insiders that there will only ever exist 21 million bitcoins, i.e. 2 100 000 000 000 000 (2.1P) Satoshi, with the word Satoshi in Japanese characters (in Japan-red). I also have a design with the absolutely exact number, but 21 with a lot of zeros looks nicer, and more people may recognize it, and it's pretty darn close to the exact number...
Description: Satoshi Nakamoto is the name used by the unknown person or people who developed bitcoin, authored the bitcoin white paper, and created and deployed bitcoin's original reference implementation. As part of the implementation, they also devised the first blockchain database.