Yes. You would think that for law enforcement (in a patrol car evaluating a passenger car in the extreme left-hand commuter/express lane) sticker locations could be something like:
- somewhere on front-bumper (so CHP personnel could see the sticker in their rear-view mirror when in front of the passenger car)
- front-right and/or rear-right (so CHP could establish compliance when traveling to the right of the passenger car)
- somewhere on rear bumper (so CHP could see the sticker when in back of the passenger car)
I assume CHP has offered suggestions over the years, leading to the changes in sticker locations we've seen. They would know best, though I would say that three of the "large" stickers (Why the difference in size?) should be satisfactory (for front bumper, right-side, and rear bumper), and that no sticker need be displayed on the left side. But what do I know? (How often can CHP monitor passenger cars while presumably parked to the left of a commuter lane? It's possible on some highways, with CHP parked in special limited-access U-turn passageways intended for emergency vehicles, but probably rare.)
In actuality, does law enforcement spend much time on this issue? I would assume that most HOV lane infractions result when a driver is first driving dangerously, alerting CHP to a bigger problem, and that an HOV lane infraction is tacked on as "icing on the cake."