A friend sent me this picture of a bus, and after some digging I found the credits for it:
Artwork by Magda Sayeg (Photograph by Cesar Ortega)
In this crocheted masterpiece, artist Magda Sayeg yarn bombs an entire bus in Mexico City. Considered to be the mother of yarn bombing, Magda did her first solo exhibit in Rome at La Museo des Esposizione in the summer of 2010.
Here is Sayeg working on the bus:
I also discovered that yes, there are yarn taggers. And this is a "tank tag":
And there is helpful advice on this blog:
Do you think they will start to check ID before they let us buy yarn? *cackles*