Another internet rumour spread by well-meaning but uninformed individuals.

The DC region tag does not ask for blood type.
It asks:
Name/address/phone
Emergency contact
Personal Physician
Medical history
Medications
Implants
Allergies
Organ Donor
Misc (tetanus)

Most regions ask for more than this, and keep it on a card that is not private, and will not necessarily be transported with you. The helmet or helmut if you prefer does make the trip.

Al Bell
DC Region Comp Committee