TIPS
T - to
I - insure
P - proper
S - service

Here in the states there is a miminum wage law. Employees have to be paid a certain amount "EXCEPT" certain service workers, like wait staff, bartenders & the like, it doesn't matter if their employer is cheap or not, they get & are expected to get tip on their service/performance. They can get paid far less per hour than the mininum because they rely legally on tips, this is as per IRS laws (they are supposed to be taxed on their tips too. Go to almost any bar or resturant in the US (fast food types are not included) & you're expected to tip ('If you can't or won't tip don't go out!') generally between 10%-20%. If I go out to a session (I only drink soda/pop) which at times cost anywhere from $1-$2, sometimes I'm only charged for the first drink. I leave a tip the size of that I would leave if I were buying a real drink. At one session the players drink for free at others they pay for the first at others the session leader buys drinks at random at others you buy no matter.
I've been bought drinks at sessions some times for singing (I was not what in the UK would call a floorsinger, we generally don't have that here), sometimes at a small session some patrons may buy a few rounds for the players but I haven't seen anyone single out one player & tip them that would be rude but I've never here seen a paid musician get tipped, maybe a drink. Some performers when playing bars may ask if there are requests & if there are "write them on a ten dollar bill & send them up", they may get tipped for doing requests but it's not to common like that, though it does happen from time to time. If in a swanky resturant & there's a strolling musician & you make a request when that musicain comes by your table & you stop them, you should tip them, in that case. I've also seen the hat past but not by musicians that are getting fairly paid. There is a session in the San Francisco area where the session leader passes a hat & you'll be embarassed if you don't put in, I don't know if the hat money goes to the musicians, to the session leader(s) & I don't know if the session leader(s) gets paid by the bar but that's also very uncommon. When playing outdoor dances or parties weither paid or not a tip jar is not considered unsocial either way, paid or not, wedding parties are different they may get tipped by whoever is paying them for a job done extra well but again not usually by a patron. So in general, paid musicians in the US don't get tipped while playing a paid gig under ordinary situations

Barry