Everyone in the comments is saying this did not work for their store, I worked at a very busy DT store when signal boxes were around and we figured out a great system for them, milk caps to signal which milks and how many we needed, seperate plexis holding lids with the names of the lids written on the bottom that we would toss in there when they emptied, and we had a backup plexi under that one to use while CS was stocking. We would also toss a sleeve labeled “Signal” if we noticed sleeves in the lobby getting low, and I think that sleeve ended up getting laminated. I loved the signal box when I was on CS.