Although it's true Legendary accounts are big targets for hackers, posting an address in the signature won't help for security reasons as it can get changed & changes to the signature doesn't get recorded, unless Theymos as a custom script.

I might be wrong, but I'm pretty sure it doesn't get recorded, at least when I did my bit with smf it didn't. Posting an address in the body of a post, personal message is different as they can be saved. I believe on the older versions of smf you could only save messages if at least 1 of the recipients of the personal message hasn't deleted it. If they have both deleted it then you couldn't recover it. I'm unsure if that covers this version of the forum though.