What would these markings represent? Structurally unsound? Hazards? If a building is posted unsafe for firefighter entry then it seems that the building should be razed, no?
On the eve of the Worcester anniversary the local news picked up on the marking program in place. For a long time the FDNY has used the 'x box' system. Wash., D.C. uses a similar marking system and Newport News just started their program, a year ago this spring, through their city fire marshal. Some systems are elaborate, identifying certain allowed operations; others are simple, like the photo you posted above.