MILW time signs

Someone mentioned that the Q used signs hung from the doorway on the last bilevel of the train so commuters could identify their train. I found some on the MILW side of CUS, and they have a time and the letters "WL" as well - what does this mean, and who do I speak with to liberate these signs? They are hiding in plain view under a pile of dust, so its not like I'm snooping around or doing anything illicit to find them - just walking around the public parts of the terminal.

I remember those old "Q" signs, but I never knew similar types of signage were used on the old Milwaukee Road, that's news to me. Since the Milw operated two lines, I'm guessing "WL" meant "West line" perhaps?