If they're stamped tin, and you found them in a rural/farm area, they could be bovine/equine vet meds. I find a fair number of them with a rubber section in the lid for a syringe.
Does it reflect light, like a cat's eye? Back before reflective paint was a thing, old traffic signs were studded with those to make them more visible...
If so you are looking at a baltimore loop seal for bottles. Used from 1885 - roughly 1904. Took me years to find out what the critters were. I found this broken bottle two years ago.