Type of death certificate required

My mother died and left her Series EE Bonds, which are registred in her name only, to her grandchildren. Do they each need an original of her death certificate to have the registration changed or would a copy of the original suffice? Tom's response If you send all the bonds and re-registration forms in together, you'd need just one copy of the death certificate. The copy should be certified to be true and correct by the issuing office or official. The office's or official's seal should be visible on the copy.