Got a question, how would everyone react to PB having gang tattoos? My head canon until we learn more about PB is an orphan that they were a gang member to make ends and saw magic as their way out.
Probably less dramatically than you might think! When you break down what a transplant normally is - an illegitimate descendant of a mage family in whom the Gift spontaneously manifested - and combine that with the fact that nobody knows who the PB is or who they're descended from, it's a fairly natural assumption for the cast to make that the PB / OT might have had a tough life before coming to Hightower.
Adelais wouldn't really react to something like this at all. She'd mentally file it away and never speak of it again, unless the PB seemed like they wanted to discuss it, in which case she'd be happy to talk it through with them.
Eleanor and Finlay, our sheltered duo, would be understanding and sympathetic, but would have slightly different angles on it. Finlay wouldn't understand and he wouldn't pretend to, or try to pry - he'd assume it's a door the PB has closed behind them, and doesn't want opened. Ellie, meanwhile, might start to draw a lot of conclusions about how this explains why the Pactbinder is so capable in a crisis. She'd be intrigued, excited and worried all at once.
Layla would want to know everything about gang life - she'd be super intrigued, maybe insensitively so (albeit with good intentions). The PB's already the most interesting person at Hightower, then they go and add a mysterious criminal past to the mix!?
Marcus would probably 'get it' the best of all the cast! He's obviously very far from a criminal or gang member himself, but he was a bit of a rebellious teen and he's met people from other walks of life through groups of mutual interest. So he at least is working off a realistic idea of what it means to be in a gang, versus a kind of vaguely dramatized movie/TV show/book/newspaper driven view like some of the others.