I work in a bar at the moment (at least for another few months), and even though it's filled with executives and corporates we do occasionally get a younger crowd on the weekends.
I've flirted with girls when they come in, gotten numbers and actually called some of them after work. It is my job to make customers feel special, talk to them about absolutely anything, it is somewhat taboo to actually proceed with anything after serving customers though, but it doesn't really matter if things are outside work.
Cyth, I think you should just get talking to her. It's kind of their job to talk to you, so charm your way right there. Somehow get her to write her number on the back of the napkin, you'll know that she's keen if she's the one giving her number to you.