How old are you, anyway!?
Oh, I remember old Fedya when he was a young'un.

Why would anyone go to the trouble to get a yellow ticket, and not just offer their services on the sly... it's not like they want to get a certificate or something, I am pretty sure they are not happy about their occupation.
I guess prostitution was only legal if you had the yellow ticket. I'm sure they're not happy about their occupation, but you wouldn't want to get in trouble with the law, would you?