Bartenders are basically untouchable until you master the game. This is because, given the sheer number of patrons they serve, they've seen and heard every line.
For this reason, when you DON'T mess up by saying or doing the wrong thing, bartenders will sing your praises. They will make it extremely obvious that they are interested. This will be mostly apparent by the amount of attention they give you, and the amount of time they spend in front of you while holding eye contact. If they are at the closest point to you, put their chin on both hands with elbows on the bar, and flutter their eye lashes, know you are in like Flynn.
Unlike strippers who give out their number to practically anyone who asks, bartenders rarely give out their number unless they are interested. Unlike strippers who are impressed by $20 tips and up, bartenders are impressed by $5 tips and up. They are equally broke so be generous. When you get great bar service at a steakhouse, and the place isn't crowded, and she is interested, it will feel not unlike a date. She will cater to you like your mother if she is interested. When she's not, she will seem to always be at the far end of the bar.
When bartenders are interested they will say things like "So do you have any big plans for the week?" or "There is a show playing and I've been wanting to go". You need to move quickly in this situation because they often go home with the busboy due to convenience. You generally need to have another wait staff member who also likes you, and the two of them have to agree on you. They will talk about you in the back. By this point the entire staff will know the situation, and you are either "that hot guy at the bar" or "that guy who won't take a hint".
Beware of this trick: if you ask for her number and she hands you a pen and paper to write yours down. Insist that she writes hers down or it's LJBF.
The easiest way to test her interested level is to go back a second time. If she remembers your drink, good. If she remembers your drink and calls you by name, great. If she ignores you even slightly, it's over.
