Most of them are at the base of structures like signs and trees. In a few places it looks like the Z projection is overlaid onto the video with the wrong perspe

Most of them are at the base of structures like signs and trees. In a few places it looks like the Z projection is overlaid onto the video with the wrong perspective, so it's hard to tell. My guess is that they are generic stationary object recognition tags that serve as hints about what isn't part of the road.