Yes, ok. Formed in 1939 in WK4.
Is it common to put a bar over the "m" in stam?
The bar means the "m" should be doubled. it should read "stamm". I like it, makes the disk more interesting IMO.
What type of weapon would this unit use?
Here is the unit information from Lexikon der wehrmacht Panzerabwehr-Ersatz-Abteilung 4 - Lexikon der Wehrmacht
You would have to figure out what time period the tag is from and what weapons the unit was trained in the above link can get you started, but probably some armored anti tank vehicle.
+ good one!
the double stamp on the blood type seems different to me.