The typical view of Pennsylvania Railroad position light signals mounted on a steel angle iron signal bridge is one where two heads are mounted on a short pole that is in turn attached to the signal bridge structure.
But what if I were to turn this view...about its vertical axis.
Do you see it yet? How about now...
As is now obvious, the original PRR concept for mounting the then new position light signals was to place the lower head on its own little mounting mast, forward of the upper head. In the above example at the late CP-PENN, this provides all around maintainer access to the both signal heads to replace bulbs or clean the lenses, although period signal bridges would have afforded this access only to the upper head. As time went on, the more common single pole mounting became standard. Still, the earlier step-mounted position lights were left in place.
Above we can see the eastbound signals at the late CP-GRAY with an original configuration step mounted PL in the center, a modified step mounted signal with a Safetran lower head on the right and a standard mount PL on the left.This reflects the PRR Main Line 2x2 Rule 251 configuration that was later altered by Conrail to double track Rule 261.
With most of the PRR position lights now removed from Class 1 service, the best place to catch stepped position lights is on Amtrak's Northeast Corridor between Philadelphia and Wilmington. The above example are the northbound signals at HOOK interlocking in Macrus Hook, PA. The stepped signals seen below are the southbound signals at BALDWIN interlocking in Eddystone, PA.
Like the previously discussed compact position light mounting, the stepped mounting is another one of those things you might never have noticed until it was pointed out.
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