While signature stamps are a fairly ubiquitous piece of office equipment, a lot of people still question their place. It may make sense for a secretary to use one to sign simple letters on behalf of her boss, but it seems less obvious whether a signature stamp is legal for checks or other important documents. That being said, signature stamps are entirely legal, even on notarized documents, as long as the person using them is authorized to do so and state laws are upheld.
On its face, this question seems rather simple, but legally and historically speaking, it's a little more complex. That's because while most people think of a signature as something created by a person writing their name (most often in cursive), that isn't the only way someone can sign a document. The legal definition of a signature is generally based on the intention of the signer and whether he intended to authenticate the document on which the signature appears, not how the signature is actually made.
While it's far less common than it once was, there are still quite a few illiterate people in the world, not to mention those with handicaps that physically prevent them from signing their name. For these people, a simple X or another mark will suffice as a signature. Alternatively, a coat of arms or another image that's drawn, stamped or embossed can count as a signature if its user intended it to serve as one. This makes sense historically as the clergy and nobility largely relied on their seals rather than signatures to authenticate documents, and the illiterate masses would often use just an X.
Just as a person could still use a seal, a coat of arms or an X to sign a document, a rubber stamp signature is legally binding as long as the person who used the signature stamp was either the person the stamp represents or someone legally authorized to use to the stamp on her behalf. As long as the person who the signature stamp represents intended to sign a document, the signature should be acceptable. This is why it's so common for companies to use signature stamps.
Of course, as with any legal matter, things are never just black and white. There are two major signature stamp legal issues that can arise, the first being what happens when it's used without permission. After all, a signature stamp only counts as a legal signature if it has the intention of the person being represented by the signature.
Misusing or falsely using a signature stamp is considered fraud as it involves falsely representing that you have the permission of the signer. To stop fraud by signature stamps, some states have specific laws about their use, ensuring that authorized users of the stamp have written permission or a signature stamp authorization form. Some states even require these to be notarized.
Similarly, some (but not all) states have special rules for notaries to follow if they're to validate a document when a signature stamp is to be used. These extra steps are to help prevent forgery and fraud. While state laws may vary, they may include details like requiring one or two witnesses to observe and sign that they saw the signature stamp in use, or to have the notary note on the certificate that the signature was made with a stamp and to name the signer. If you need to have a document notarized and you intend to sign with a signature stamp, be sure to mention this to your notary ahead of time so he can properly follow state laws.