Here's a product on ebay. It's a keyring to hang off your minsistry bag.
I don't see why it doesn't say Attention I do not accept the primary components of blood—namely red cells, white cells, platelets and plasma. However fractions of all primary components are permitted. I'm not entirely sure what that means but if there is a medical emergency then you can always ask the Hospital Liason Committee who are the guys in the foyer in the suits carrying Bibles.
Maybe there wasn't enough space.