sign is
uchar pat1[] = {0x01, 0x30, 0x82, 0x01, 0x13, 0x02, 0x01, 0x01, 0x04, 0x20}; //old wallet  (<2012)
uchar pat2[] = {0x01, 0xd6, 0x30, 0x81, 0xd3, 0x02, 0x01, 0x01, 0x04, 0x20}; //new wallet

exsample:

wallet.dat or disk open is hex editor

01308201130201010420 -sign later [key]
good luck