Does anyone here read old guy?

Work with a great old guy who does all the drawings. I think he learned drafting in the army or something. Anyway, I can almost always tell what he’s written but I’m stumped here. Bottom word is “Top,” then left to right above that we have hot water heater (“H2OT HTR”), and then?!? Can anyone tell me what “PLBalum” means, and best guesses on whether I should install it, fix it or take it out?

(Ground floor passageway between garage and living area, Northern California 1940s build.)