E-Views - Emergency Vehicle Intersection, Early Warning System
Monrovia was a test site for the E-Views displays (the square display signs on the street light pole just above the street light). They were installed at 8 intersections in 2001. I've seen these signs in action a few times and think they're a good idea.
See this press alert and this press alert for background info and a description of the system. The 2nd press alert also has links to additional photo's.