French tankard?

I cannot take a pic at the moment but wondered if the following info would be enough to go on till I’m able to. I have what seems to be a French lidded tankard which has been in family for years and I’ve always been drawn to it for some reason. As a child I was fascinated by the no 4 and the letters P and M (in capitals) on the lid. the no4 sits between the letters but slightly higher. It says demi litre on the front and
on the base are 2 crowns (?) below them it says LERCLERC A LILLE HUMBERT. There a 3 small dark circles with letters in on the side of the rim but they are very faded and hard to work out. I do realise a pic would be so much more helpful sorry but couldnt resist trying when I found this site. thanks