Answer:
Assuming that your deposit customer is claiming that his/her (the drawer's) signatures were forged, you've gone past the deadline.
The deadline for forged, unauthorized or missing signatures of the drawer is the business day following presentation.
In general, that's the deadline for anything that you should be checking that has to do with your deposit account and your relationship with your customer, such as balance, stop payments, drawer signature, date. It does not affect things outside your ability to determine, such as endorsements.
First published on BankersOnline.com 8/12/02