Here are a couple ideas I have for designs for t-shirts:
There’s an automated register at the local supermarket that has a slit in it labeled “Cash Acceptor: $1 $5 $10 $20 $50 $100”. I think just the phrase “Cash Acceptor” printed on women’s t-shirts would be a big seller.
Also, there’s a sign on a gas pump near my home that says: “Contains Up to 10% Ethanol” in big block letters. I think that would go well on a t-shirt, too.