Union dues stamps! Thanks for sharing, sopotsopot.
I found these items recently, tucked waaay back.

International Association of Machinists. These were my grandfather's. He worked as a civilian fireman from the 30s to 1967 at NAS Moffett Field (Naval Air Station). I'm pretty sure the photo below was taken right about the time he retired. Note the good-looking kid on the right.
