Vermont law calls it an official stamp. It may be a rubber stamp or an embosser, or even an electronic process or image, but the official stamp must "be capable of being copied together with the record to which it is affixed or attached or with which it is logically associated."
This means that if you use an embosser and want it to count, you'll have to use an inker on it.
Instead of using an official stamp, the notary may clearly print the notary's name and commission number in the certificate. (Some states put the commission expiration date in the stamp; Vermont requires the commission expiration date always be in the certificate.
What happens if you use a rubber stamp and an embosser, and don't ink the embossed impression? The law doesn't say.