"At the lower end of the categorization system, sources in Category 5 are
the least dangerous; however, even these sources could give rise to doses in
excess of the dose limits if not properly controlled, and therefore need to be
kept under appropriate regulatory control. " (page 5)
Lightning preventers are typically category 5 sources. (page 27)
The misspelling ("Do no open" vs. "Do not open") suggests that this was not mass produced.
It would be interesting to know:
1) What is the word that begins "CH" on the white insulator? (I'm sure it's not "Champion".)
2) Is there an electrical connection between the metal capsule and the ground connection? There probably is, but you can't tell for certain in the photos. If there isn't, this may be a triggerable spark gap.
3) How big is it? Perhaps 8 or 9 cm?
If polonium was used, it long dead.
I doubt that it had any use as a lightning arrestor - you don't need anything that fancy for shorting lightning.
Okay, so 60 or 80 years ago, someone infused or coated the anode of a Champion spark plug with a radioactive isotope and then sealed it up with a small canister. I believe that would make it a high voltage rectifier - that has long lost its uumph.