Symbols on the ground are infrastructure, you should not be able to patent a thing like that. Imagine every company that makes vehicles having to license someone else's tech in order to be able to use public roads, or a huge variety (one for every brand) of competing symbols polluting the roads.
Signs on roads == traffic signs, open formats and readable by everybody.
The person who invented the original traffic signal patented it in 1923 (http://www.google.com/patents?id=EHJoAAAAEBAJ&printsec=f...). The idea was unique, novel, and non-obvious at the time. It's easy to see an invention now that is ubiquitous and say that it's obvious.
Signs on roads == traffic signs, open formats and readable by everybody.