Agreeing with Creskol... it is a clothing hem weight or coat-tail weight or curtain hem weight -- sewn into clothing to keep a woman's long skirt (or man's coat-tails) from blowing around embarassingly on a windy day, or keep your curtains hanging straight down. Although they date back to the mid-1800s, they are still being manufactured today, so they are impossible to time-date, unless they have a machine-molding mark, which means it was made in the 20th Century. In more recent times, there are also square-shaped ones.
I knew I had seen something like it somewhere before, turns out there's an older thread on here where a fellow had a couple.
