Brian and Paul,
Since the photo was found at the bottom of a Coast Guard file cabinet, I tend to agree with Brian. Also consider that the Coast Guard was heavily involved in both port safety and port security during WWII.
Both officers and enlisted men wore the same uniforms as the Navy, except for insignia and sometimes the "Donald Duck" hat for junior enlisteds (but also the Navy "Dixie Cup", you see in the photo). All I can really tell you about the SP facing the camera is that he is a second class, though his specialty is unclear. Chief Petty Officers and officers usually wore Navy khakis.
Now that I have your attention, I will share a story about legendary Coast Guard Captain Higby (later promoted to Admiral upon his retirement). He was, IIRC, head of port security in Long Beach/Los Angeles during WWII. Higby could be a terror. Once he was inspecting a bridge with one of his subordinates who was responsible for that structure. Sitting right on the bridge was a box clearly marked as dynamite. Higby pointed out the box with great indignation, then drew his .45 and put a bullet right through the box. His subordinate officer almost fainted. The box was, of course, empty and had been placed there by Captain Higby just to make a point.
I knew Admiral Higby slightly. He used to wander around the District Office in Long Beach in his very senior years (like 85 or something). He often used the restroom outside my office to change into swimming trunks and a bathrobe before going down to the shore for a dip. He was quite a character.
Now let's get back to boxcars.
Garth Groff 🦆