I've been reading that in the US there's a thing where certain kinds of people leave fake bills with just a corner showing just the dollar amount and the rest hidden under a napkin or peeking out of the check holder, but upon closer inspection turns out to be not real money. Such fake bills contain christian-adjacent texts which read things to the effect of "Jesus's love is more important than money".
I don't think anyone can tell for sure if any such person who leaves these fake bills does it as a way to propagate their religious beliefs, or to be a cheapskate with an "excuse", but the bottom line is they're leaving fake bills instead of real bills, and it's not cool to the servers.
Some say that the Secret Service will only investigate if the bills appear to be at least not obviously fake in full view, but the way these bills are used, only the real-looking portion is left in the open until the server comes over to collect them.
Is such use of "Jesus money" illegal? Can servers (or managers) of restaurants call the police on the customers for doing that?