I have this suggestion from a client for your consideration:
He thought it might be useful to change the colour (or some how notify the manager) of an open table once the waitron had printed the bill for the first time.
For example, if the restaurant has specials on a particular day where everyone comes in for say 2 castles for the price of one as an example, some small bars don't have a dedicated bar printer or barman, an unscrupulous waitron might print the bill but not ring off the sale, he would collect the cash and then do the same for the next person.
Thanks