While on a tour of Colonial Williamsburg years ago, our guide took us to a tavern and showed us the large chalkboard at the end of the bar. He pointed to the large "P" and "Q" written on the left-hand side with names printed beside them. The number of pints and quarters of liquor or beer they had charged to their account was listed beside their name. It reminded the men as they entered the bar to "mind their Ps and Qs." It's what they owed.