discharge tube
Congratulations Fran. Not only did she answer the "What the heck is this?" correctly, she was the first commenter.
Here is the original item:
It is of course a gas discharge tube. You put these tubes in there (as shown above) with helium or neon or whatever in there and it excites the gas to give off light.
Honestly, we have like 10 of these things laying around. Some of them are newer and say "Danger 5000 volts"), but these older ones say nothing. Here is an example of one of the first ones I saw.
I didn't figure out what it was for a while because most of the ones we have don't have those…