It would depend on the girl. If you give her a note, two things could come out of it,
One: she gets wierded out and would never want to wait you again.
Two: she thinks its cute and goes for you.
How much do you know about this girl? Is she single? Because if she's not, outcome one will more than likely occur. If it was me personally I would think the note was cute, but a better idea is to get to know her better first. This is hard to do in a work setting, so I suggest catching her on a break or after her shift.
Dont be to aggressive in trying though, she's at work and does have a job to do.
Dude..what's the difference if you ultimately want to tell her? and since you want to tell her then show some class.It's not like she won't reject you if you slip a note.If she has to reject you then she will confront you and ask you if you have slipped that note.Then what will you say?
Unless it was a guy you were hitting on it wouldn't be gay but a little cowardly. If you're really into this girl than by all means bro let her know. You can do it , trust me and think about it the worse thing that can happen is that she says no. Just believe in yourself my friend and after that nothing can go totally wrong