Doug,If only that were part of the rules. Other places say it is fake.
It is confusing as it is not part of a rule book but the NFL Operations Manual. It is "Page A62 of the NFL Game Operations Manual." and is a policy not a rule like holding or blocking in the back. If you Google the above you will find that the NFL has a policy against it but chooses not to enforce it. I choose not to watch NFL football. That's my policy.