If there was a way to hack sign placement forceop might work :p I doubt it's possible but having a hack that can place signs with commands in them would be the most op thing ever
I'm pretty sure that when the first ForceOP hack came out, it was mainly used in books. The command would be hidden in the book and when an Admin clicked a link or something in the book it would execute the command in the book. Signs, if ever they are updated with a command, could be a big problem though :P