The Union Switch and Signal Company favored by WM was noted for
inventing an electro-pneumatic signalling system in which compressed
air powered the switch and the signals.
The number of tanks and the piping here indicates this had been one of
the installation locations of such a pneumatic system for at least the
switch (points). This is the only trackside survivor I've seen anywhere
in the Baltimore region.
Vines shroud these artifacts during summer, and even during non-leaf
season they hide details. A bit of digital editing helps sort
The US&S book linked below contains dozens of pictures and details
but lacks a photo of an installation of these components. The closest
in appearance, by coincidence, is the diagram on page 85.
US&S Electro-Pneumatic Interlocking book (PDF)