Have you been seeing the Bitcoin signs posted on ATMs around San Francisco? In the past several weeks, Bitcoin signs and stickers have been seen adorning various ATMs and Apple buses all around the city, presumably as a reaction to Apple mysteriously dropping Blockchain, the most popular Bitcoin app, from the App Store on iTunes.
Bitcoins are an electronic form of currency which people can send to each other and use to pay for goods and services--anonymously. No banks or banking services are involved in Bitcoin transactions, which makes it a preferable way to transfer money for some, and a controversial one for others.
An Instagram user named crytograffiti (most likely named because Bitcoins are transferred using crypotography, very clever) has been posting pictures and videos of the various sites around the city where Bitcoin graffiti can be seen, presumably the user's own. The only identification the user provides for themselves (aside from their punny username) is, appropriately, their Bitcoin address.
Check out this video of an Apple bus getting, um, redecorated: