The Davis Square Community

After a fair bit of scouring in the archives, I regret that I found nothing related to my question, so:

At what level of visibility would an artist earning money/tips for (temporary) henna tattoos in davis square plaza start getting into trouble?* I imagine this would go also for musicians. I am not good enough or interested enough to set up even a blanket. However, while I was doing a tattoo for a friend --we happened to be sitting on the metal tables by JP Licks, which I can't imagine would be a problem-- a passerby was politely interested and might well have gotten one if I had encouraged her. It would be fun, after all, to draw for tips! I could imagine being out there several nights a week, drawing sketches on paper, accepting the occasional passerby for a tattoo, earning coffee money, but then maybe I'm on crack.

I am aware of the health and allergy concerns of doing this kind of work, and I'm not qualified yet to offer this service "professionally" to the public at large, but I wondered what level of organization/regularity constitutes the need for some kind of permit. I participate in ArtBeat for other art, and realize that we can't all be hawking our wares all the time, or the pleasantness of the square would be somewhat diminished. So maybe it's a bad idea socially.

Thanks!

* FYI: Henna is a plant which releases a brownish dye into the skin and lasts for 7-10 days. Safe, no needles Very portable.