I don't know if they provide a letter of guarantee for sending funds between note addresses. If they do so, the other way is people send their funds to your note address and then send you the letter of guarantee.

If a trusted member of the forum sends you a letter of guarantee or a note private key, I think that's enough.
If a newbie who has created an account recently is claiming funds, you should ask him to provide more evidences like the LoG of the deposit. You should not accept the claim, if the deposit has been made after your today's announcement regarding claiming funds from the escrow. It's easy for the person who access to the private key of the signing address to come here and claim funds.