Should have mentioned the size. It's two inches in diameter (excluding stem and crown), just like a real pocket watch. Took another search break before posting this and look what I found:
http://www.geocities.com/skm46morris/Watches.htm
You'll have to scroll down a ways to see it. But there's a story that explains these that is somewhat similar to my Uncle Raymond's explanation. This time I googled "pocket watch made of glass" instead of just "glass pocket watch."