I would say the same about anything on the road that isn't specifically for safety/traffic shaping.
> They're not planted to catch your attention in ANNOYING ways.
Even some of traffic shaping signage are specifically designed to be that way.
More importantly, this is about a freedom of expression. If I want to yell about my fruit farm or hold a sign for your product; is that different? How does the freedom to express yourself contend with some idea of limiting "commercial advertisement"?