With the spread of debit cards, I would imagine that the number of merchants that don't take CC's are less than 10%. When we were in New Zealand, there were zero merchants that did not take debit/credit cards, even dinky antique stores and campgrounds. I don't look for logos in the window, because many restaurants don't display them. Unless the sign is at eye level before you walk in the door, it could easily get lost in the restaurant decor. How hard is it for a waiter to say, "The specials are fried squirrel, bat stew, and we are a cash only restaurant." ? That gives you the length of the meal to figure out how to pay.

I would have tipped significantly less or not at all.