If it’s a kisser button it locates your cheek weld exactly the same place each time by having a reference point that touches the corner of your mouth. Similar (but much more modern) devices are used by tactical (“sniper”) competition shooters so they can quickly acquire sight picture every time in exactly the same position.

Just my guess.

Steve

I can make out “PATD” on the side of it, is there more to the date?

Maverick