if you can find it manually, just find it and compare bytes with previous patches.
For example:
Patch one
FF DD FF BB FF CC
Patch two
FF AA FF BB FF CC
Patch three
FF AA FF BB FF CC
your sig would be:
FF 00 FF BB FF CC
mask:
x?xxxx
with the ? indicating the non important bytes(ones that are not consistent throughout all patches)
bad explanation but you should get the general idea.