More and more, I see these “boxes” mounted beside the traffic light. They look like they could flash a short message, or perhaps flash “CAUTION” or something? They look a bit bigger than the electronic “X” sign used to denote reversable lanes. Does anyone have a clue what these are? I will say these have surfaced in the last year, at best.
Could be to flash “No Left Turn” during peak hours. We have these here now in LA.
Ditto this; these signs are all over downtown Milwaukee as well.
If your state allows turning right on red they could be electronic signs prohibiting this (i.e. No Turn On Red signs) at certain times.