Yeah, it would be a good idea. I would even go a bit further:
Main problem is when people add multiple compounds, they forget from time to time to change one of the lists. This way Bomb Diamond sneaks into the compound.
It would be nice if first positions in dropdown lists would be blank instead of Bomb Diamond. And system should block adding compund with any blank postition, giving back an error message, something like "You have to choose a created item" or "You have to choose compounded item".
It would save a lot work for moderators, and would be much more clear for people to tell wich list thay haven't filled up yet while adding compound.
Having a signature is like keeping a gremlin.
Just don't overfeed it, don't make it wishy-washy and you'll be a good responsible Signature Keeper :]