Except as otherwise provided in FC505.4.1, and except in buildings protected throughout by a sprinkler system, in a Group R-1 or R-2 building or occupancy with more than eight dwelling units on a floor, each dwelling unit shall be identified on the door jamb on the public corridor side of the door by an approved fire emergency marking, not more than 12 inches (305 mm) from the bottom of the door, indicating the dwelling unit number and/or letter.