You are mostly correct, especially for people following you. The "Hybrid Synergy Drive" tag in the rear is too small for people to notice while following you. The side tags are much easier to spot, but at highway speed usually only the passenger of another car will see them. The best chance of being noticed is while being stuck in traffic. On the trip home yesterday (sitting in traffic) someone actually noticed me and rolled down his windows to ask questions.

For the record, he didn't know the Camry came in hybrid flavor...