I had heard this was used as a control, but always thought it was too weak to help much. Around here, I only remember one place having such a sign, and that was decades ago.
You can hand a customer pretty much anything and claim it's a receipt. At the pizza place I worked at, the receipts were hand written, with a carbon copy that had serialized numbers on them. The previous management had obviously been doing some skimming. The had a whole week were they sold $200 in pizza, that's like 20 pizzas. I had figured they got a batch of order forms somehow that were unaccounted for. Then at one point realized they could have just used anything.
Someone in the know would immediatley pick up on the fake receipt. And they could do that using the serial numbers, even if they were using stolen order forms. So the whole tracking of receipts doesn't really help.
Even in today's printed receipt world, it's not that hard to get your own printer to fake some.