I think the concept of the line of death, from browser security UI design, is relevant here. The space outside of the highway right of way is completely uncontrolled and the Tesla should know better than to look at a billboard hundreds of feet up in the air for regulatory signs. The MUTCD has rules about where signs are to be placed--look only in those places.
[1] https://textslashplain.com/2017/01/14/the-line-of-death/