There is nothing in the text of The Giver to indicate that family units were assigned any specific type of number, address, or other distinguishing identifier. Family units were created through assignments given by the Committee of Elders, who approved arrangements for a man and a woman to live together and determined the assignment of children to the couples.
Because the need for conformity, structure and organization was central to the functioning of the community, it is reasonable to assume that all living quarters for family units were probably identical. There probably was some sort of identification to differentiate between specific units; a number such as an address would be a possibility. Family units may have simply been identified by the given names of the father and mother of the family.
They were marked by birth order.