I’ve only seen these signs in Irvine. I suspect that says something about them:

Perhaps an important warning to drivers, but it’s not a well-designed road sign. There’s too much detail, for starters—detail you’re not going to see clearly zooming by at 35 M.P.H. Compare to the stick figures of the standard school crossing sign, or even to the bunny crossing sign.

More importantly, the cues chosen to identify senior citizens are temporary, in the sense that they’ll look dated not too long from now. Why a hat, for instance? Well, people often hold onto the fashions of their youth, so the only men you’re likely to see wearing a full-brimmed hat today are old enough that their fashion sense was formed when hats were still popular. Sure, it gets the idea across today, but 30 years from now, no one is going to associate fedoras with old people any more than we associate stovepipe hats with old people today. It’ll be associated with history, not with age.

Sure, you could say the same about restroom signs—women don’t wear skirts all the time anymore (and how do you deal with kilts?)—but skirts aren’t likely to disappear or swap genders anytime soon, and the standard signs are simplified to the point where you have to be really pedantic to seriously suggest something else.