You don't even need to sign anything sensible at all. They almost certainly aren't going to check, and if you try to defraud the restaurant by refusing to pay, you might find yourself in trouble, regardless of signature.
On the contrary, I’m not trying to defraud anyone. I’m using a custom signature as evidence that it actually was me; if someone swipes my card and uses it somewhere it’d be obvious that it wasn’t me because the signature would not match the consistent deterministic gibberish that the real me would have signed.
It’s also a habit to sign actual restaurant receipts with a signature that isn’t my real one but a specific one for restaurants.