I find the signs on the HOV lanes to be misleading to those who haven't dug into it like local owners. The signs just say "AFV allowed" and reference the statutory code. If a non-local were coming through town, I highly doubt they would realize that the code requires a special tag, but would assume that anything classified would apply -- so that may be part of the reason the enforcement is lacking in many cases.
I also have an issue that I can't have the AFV tag personalized, so I had to decide which was more important to me. We ultimately decided that we don't drive through downtown enough that the AFV makes a difference (and usually when we do, we're together), so we went with the personalized plate, but it's stupid to have to choose.