For those who might not be up on their obscure references to the sex trade, the vanity plate "AINTESY" is a reference to the expression "Pimpin' ain't easy," first made popular (I believe) by Big Daddy Kane.

(I know this only because I used to watch Chappelle's Show on Comedy Central, where it was one of the questions on the game show skit "I Know Black People".)

Part 1

Part 2