Yes you do have to sign an indemnity and this is why I suggested actually calling into the bank.
Most drafts now have automatic crossings on them so there would be no doubt about the correctness of the crossing.
If it were lodged to the UL a/c after it had been stopped it would be returned unpaid. The indemnity is in case the buyer tries to process it himself, seeing as he's the only other person that can transact it.
A draft cannot be stopped for any reason other than being lost or stolen, as being prepaid they are normally taken on good faith.