Looks like a shotgun magazine spring retainer or possibly a magazine follower. A retainer would be at the top of a magazine spring and the follower would be at the bottom.
That ain't from any 870 I've ever seen.
The cat left it. Messing with you.
That's what I was thinking. Fell off the vacuum cleaner...See if there is a part missing on the vacuum that would look like that.
It is part of an apparatus used to link two jockstraps if: you are a standard-bearer, that’s what you use as a carrier and you are carrying two flags.
I’m kind of surprised no one knew the answer. In the Lone Star State it’s called a, “Texas Two Flag Bag”.