How about 1950s airplane non-toys? When we went through my dad's stuff, we found some wings that were about three feet across. On the top they said something like "This does not contain anything useful even to an enthusiastic amateur. The owner is a struggling scientist engaged in upper atmospheric and cosmic-ray research. If found, please return to <NAME> <ADDRESS>".

The skin on those wings was insanely thin. You could break it with a fairly gentle touch.