We use the stickers and little folding cardboard signs that we got from Square. Like Julie said, even if you have them plastered all over the place, some people will still ask.
I've had people staring at the Square Visa sign, and then turn to me to ask me if we accept credit cards. I've also had people staring at our price list, then turn to me to ask me how much is this or that.
Go figure, lol.