1965 Dodge Dart Charger

After a good cleaning the next rear window mecanism turned out great. Behind a part of the mecanism I found a #3! I don't know the meaning but it's part of the history!

I did some glass beading and when I did the newest J-hook incl the nut I found out that it has some kind a locking red glue or strip.! Is that a plastic strip or some kind of locking glue?