You can now use a mirror in game, either a stationary one, or a hand held mirror to see just how well your disguise is holding up. The messaging is not super duper specific, and is intended to give you an idea of roughly how well your disguise is doing.
This opens doors for a lot of different things. Sneaking off to the bathroom to powder your nose while pretending to be a mixer in the mix or a corpie working topside. Checking your disguise before leaving your apartment to go on a job. And many other things.
I don't wanna give too much away so you'll have to mess around with it yourself if you wanna get a feel for it. Enjoy :)
-- S