While I don't practice in CA, my opinion would be "No" a rubber stamp would not suffice to act as a signature unless there were extenuating circumstances and even then, I would do my best to get the Testator of the Will to sign it in person. 

Speak to a local CA lawyer to verify this analysis.

Answered by Theodore Robinson on 03.18.11.

As a forensic document examiner I can't answer the legal question. From the perspective of a document examiner, rubber stamps can be difficult to authenticate since anyone can have a stamp made. The document examiner must look for details of the stamp under a microscope in order to determine whether the questioned and known stamps are identical. A problem with rubber stamps is that they wear over time. A result may be that the legitimate stamp may exhibit different features when compared with prior uses. Analysis of rubber stamps is a specialty area for document examiners. Perhaps the best authority on this subject is Gary Herbertson, formerly with the FBI.

Answered by Michael Wakshull on 04.16.11.

Another item to consider regarding the ability to authenticate the user of a rubber stamp is that a person may own more than one valid rubber stamp with the same engraving. A rubber stamp may be accessable to multiple people if it is kept in an insecure location.

You are welcome to contact me for additional information.

Mike Wakshull
http://www.quality9.com

Answered by Michael Wakshull on 04.16.11.