I'm no lawyer but if you remove it you are in for big trouble. Don't do it.
We live in a country of laws. If they don't pay, based on the amount of the claim, take them to court.
First send them a demand letter, certified. The judge will ask if you did that. Keep the certified receipt.
If it's small claims, usually less than $2000 (depends a lot on your state and county) then you can file the claim yourself
and meet them before the judge. Get pictures, bring emails, agreements, anything you can. If you have a case and the judge is fair,
you can easily win. If they don't show up, you the plaintiff win the case by default.
If they still refuse to pay after you win, you can go to a sheriff with a copy of their last check.
If they have money in that account, he can get the bank to withdraw your judgement and give you the check.
It's a long process, it doesn't always go the way you think it should, but man, it's the education your parents couldn't afford to buy you.
You'll learn to read people and future customers real fast. "People, the toughest business in the world".
BTW, how much do they owe you? How big was the sign? Give us some deets.