I noticed that the shapes started disappearing when traffic lights were being retrofitted with LEDs. When they started doing that, they didn't simply put the LEDs inside the reflection cones behind the lenses as one might have expected, but instead put disc-shaped LED matrices on the outsides of the lenses. At least, that's what it kind of looked like.
If you watch for them, on some signal heads you can still see square hoods where the red lights were. Incidentally, they changed the standard of signal arrangement: where, before, the right and left arrows were on the outermost positions of the signal head, now it is always the red lights that are outermost, and the right and left arrows are usually adjacent to the green and/or yellow lights. This results in the arrow lights sometimes having square hoods. Some signal heads have all square hoods, as in the one pictured in the question.
Some LED traffic lights were made with the shapes, but, for some reason, even those are hard to find now. During a recent visit to Quebec, I saw exactly two shape-coded traffic lights. They used to be all over the place.
I liked having the shape coded lights because they were something slightly strange that you see only in (eastern) Canada, giving tourists the impression (even if only subliminally) that this isn't just an extremity of the U.S.
Sorry for the thread bump in case that's a big deal here.