I think that more blocks besides chests, like mob spawners, should be able to be locked with a lock sign. I think mob spawners should be locked with lock signs because they take a lot of money and tokens, and if someone is a member of your island or you are doing coop with them and they have a rank, then they shouldn't be able to steal your spawners, because they might cost a lot of money and tokens, depending on the spawner.
hellu! i don’t think the lockette plugin can really control that. however, a way to “lock” spawners is to put a door or trapdoor on top of the spawners then put a [private] sign.. or you can create a decoy sign shop, and just place the shop signs on the spawners... if that makes sense hope this helped :) have a great day! ~puposaurus