I thought I had finally figured out all of the acronyms, code words and jargon used in ads for sex workers and reviews by those who patronize them. (As an aside, I loathe the expression "hobby" and its variants.) Recently, I've started to see the term "art class" in BP escort ads in Manhattan and haven't the slightest idea what this is supposed to be a euphemism for. Searching Google and Urban Dictionary didn't turn up anything even remotely relevant. Can someone enlighten me?

Urban Dictionary didn't give any hits.  

One is that she'll play out a fantasy where she is an art class model, and you the student who is "drawn" (pun intended) to her.

The other is face painting, i.e. COF.

Or maybe she is really an art teacher and will teach you all about how to draw a picture.  (nah)

I hate not knowing something, lol - but if you ignore the 'class' part of it - ART can stand for:

if it was a misspell of "art Glass", it could refer to a bong or water pipe (she does say "loves to party" in the ad) or perhaps even to an art glass sex toy. Just speculating!

And it was a piece of art.

Could be photos/video friendly too, though not sure why not just say so.