My favorite Banksy is 'Early Man Goes to Market'
Banksy hanged it on the wall of the British Museum right next to other art from that period where it stayed for 3 days without any officials noticing.
There was a sign right next to it that said: "early man venturing towards the out-of-town hunting grounds. This finely preserved example of primitive art dates from the Post-Catatonic era." With an explanatory note that said: "The artist responsible is known to have created a substantial body of work across South East of England under the moniker Banksymus Maximus but little else is known about him. Most art of this type has unfortunately not survived. The majority is destroyed by zealous municipal officials who fail to recognise the artistic merit and historical value of daubing on walls."
He also hung his own art in the Tate Britain in London in October 2003, which was not noticed until it fell to the ground, and has done the same in four New York galleries.
He ran a competition on his website for fans to have their photographs taken with the rock, offering a shopping trolley as a prize.
The British Museum praised the way his rock was hung and the style of the sign, which was "very similar" to their own design, and it later became a part of their permanent collection. It was later being exhibited at Banksy's own shows where it had a sign saying it was "on loan from the British Museum".