Even if you sign a donor card, it is essential that your family know your wishes. Your family may be asked to sign a consent form to allow the donation to take place.
To learn how organ donation preferences are documented and honored in your town or city, contact your local Organ Procurement Organization (OPO). The OPO can advise you of specific local procedures, such as joining donor registries, which are available to residents in your area.
This answer is based on source information from the U.S. Department of Health and Human Services.