Without a picture I would say most replies given would just be conjecture. My guess would be to possibly to hold a moisture disc to keep the tobacco from drying out.
No pics. Just a memory. It was not a hum disk. I was a thin gage wire ring with a stem built into the pouch. The ring sat about half way up into the pouch. I never asked him what it was for. Perhaps it was there to hold a hum disk. Dunno