Updating my plea for information the other day, I've found out -- via a friend on Facebook -- just what those mysterious decals are. They are truss signs, which are required by law in New York State (and others). They are there to inform firefighters, in the event of a fire requiring them to enter a burning building, of the type of construction used in the building. That information would undoubtedly help them to avoid falling debris, I suppose.
The one pictured in my post indicates "Type II construction, Roof". I'm not entirely certain what that means, but my guess is that the only trusses to be found there are on the roof, and they're Type II.