I have the same issue. I have two email accounts in WLM. I want the signature on one account. I follow the directions, to Options - Mail, etc., Signature tab - advanced to find both email accounts. I check the box for the account where I want the signature to appear.

I leave the other account unchecked.

The problem is the "directions" listed in the Signature - Advanced tab. It says that 'only one signature may be selected for an account. and accounts with no signature will use the default.'

So really that means that a signature will be applied even to the unchecked account.

Does anyone really read the directions they're writing??