Just curious, but how do you know it is "clearly" a forgery?  Usually, it is difficult, if not impossible, for the abstractor to determine if a document has been forged.  We normally have to rely on the notary public's acknowledgment.

However, if you have reason to believe it is a forgery, I think you should note your suspicion on the search and explain why you believe it is a forger.  For example, if you saw 3 previous mortgages signed by the individual in question, and then you come across a deed where the signature is significantly different, I believe the abstractor should provide copies of all of them so the client can investigate further.