This mark is used on lots of German products made from bakelite and plastic, from gaine pots, fuze holders, fuzes (specially the No ELAZ55 on bottom of fuze) grips for MG42, MP40, MP44, P38, personal kit, compasses and also on some sighting items.
It is found on items from about 1937 to late 1942 and seems to have been fazed out after that, and in some cases the die has been defaced so the mark becomes illegible. The mark is believed to be a supplier mark for the plastic used to make the item in question, so this item is marked with 3 letter maker mark, the mark in question identifies the supplier of the material used to make this item. I have a list of some of these marks on my PC, I will look it up when I get home. there is also a whole page dedicated to this subject on, I think, one of the Walther P38 forums.