Signage for better tips

I've got at least one, possibly two regular restaurant gigs upcoming, and I'm thinking about how to set up signage. Right now, I have a tall sign with decorated words on it that I quite like. I have a couple of designs that are specific sizes, but mostly I let people pick small-medium-large of each design, and charge according to how big they want it. In this case, I'm being paid half my usual rate plus a meal, and I get to ask for tips and hand out cards. Also, I just checked the flyers, and it doesn't say free on them, although the other stuff they do for kids' night is free. This area is curiously low on painters, so this is a big opportunity for me to meet clients.
People that do partially-paid work, how do you do your signs, so you communicate that people should pay you differing amounts for different sized designs, but that doesn't mention pricing specifics? Any other advice you can give for this sort of gig is welcome!

If you can't set prices, I personally would be thankful for paid practice & marketing...😜. Oh, and a dinner of my choice!

Tips are never as much as I'd like, but you have regular income of sorts & can knock the socks off of potential clients!