My problem with this:
The way things are right now people will be afraid to hold symbols because other people will gank them since said symbols unlock certain areas, or have some other benefits.
Random Solutions:
-Make symbols rot at player's death (will suck because after every death they will need an F2 priest)
-Make symbols zappy to opposite alignments (difficult to implement as there are grey gods with grey symbols, but at least greybies shouldn't be able to kill someone just to rob them of a symbol)
-Make the locks those symbols open pickable.
-Make the locks only open by a person of said faith unlocking hte door with a symbol
In general, I believe symbols should be more than just an item anyone can horde.
I would suggest that imms check where the symbols of their faiths are, and if they are in the hands of someone the imm doesn't like, they start messing with him.
Example from adnd:
If you took a symbol of helm without approval of the faith for whatever purpose, you slowly feel the weight of your misgiving: It starts with a -2 to a random attribute the first few days. It moves to a -2 to all attributes, then a -2 to all attributes and an added -4 to your main stat, then sickness, nightmares, and if you keep holding on to it, it eventually killed you. If you stopped holding the symbol, but didn't return it to the faith, you were left with the -2 penalty to a random stat until you atoned to helm in some way.
Fun stuff.