All roadway signage is standardized to a Federal specification. Each sign type has an assigned code. I found this out when I was looking at some shapefiles yesterday that had all of the signs inventoried along the roads. There was a sign listed as an OM-3F. The traffic engineer I was working for never heard of that. So we looked it up, and sure enough, there is no such thing as a OM-3F. The sign was an OM-3R (see below). I will have to check with the vendor and see why they coded it from the digital photo graph as an OM-3F.

OM stands for Object Marker. The three is because it is the third class of object markers. The L, C, and R stand for left, center, and right. You will see these on the ends of guard rails and bridge abutments.