Saeviomagy
Adventurer
But, it's the same thing as the security argument. Why would the bad guys leave this type of info just lying around if it tells people about them or their weaknesses?
I always found this to be a bit of a DM crutch.
The argument for this is: security is only as strong as it's weakest link. It's blatantly stupid, for example, to write a computer password on a sticky note and stick it to your computer screen - but that doesn't stop people from doing it constantly. For that matter look at some reports of industrial accidents sometime - life-and-death matters where people took stupid shortcuts, or just plain messed around. Is it really so hard to imagine the bad guys in D&D making mistakes?