These two queries should do the trick:
code:
SELECT S_Number FROM w3t_Signatures WHERE S_User = '{$user['U_Number']}' AND S_Title = 'Default'
UPDATE w3t_Posts SET B_SigNumber = '$DefaultSig' WHERE B_SigNumber = '$DeletedSigNumber'
The first one gets the ID number of the users default signature and the second one updates all posts that have the deleted signature into using the default signature.
Unfortunately I haven't got this hack installed at my test board at the moment as I did a clean install recently. But I'll reinstall it and fix this as soon as possible.