What’s the meaning of “Consumption hung low in the air”

Common senses of the verb troop seem not-applicable here, where the sense in use might instead be a back-formation from a well-known sense of trooper, “One who endures adversity or hardship with an attitude of stoicism and persistence”; or it may be, as FumbleFingers suggests, a variant of soldier on, carry on, march on. That is, in this context troop on means “endure this adversity without letting it overcome you” .

If @Kreiri is correct, than "sock" refers to hanging a sock on the outside door knob of your dorm room to warn your roommate not to enter because you are inside having sex. Go here. The explicit sign on the door is more to the point than the symbolic sock.