I reasearched this question and I reached out to the my town's traffic and safety department and they installed two street sign, one at each end of the block where we live!

I live in NJ suburbs and saw for the first time Autistic child in Area sign, we had a handicap child in area sign. They also sell those yellow little men with flags a lot of people have that say watch children. If local representative won't help go to your state representative, if they don't help write a letter to the governor.

I can't really find much info about signs online. We have them here in Minnesota. They Say "Autistic Child Area".
Not sure if they make much difference. I would say put the focus on your doors and proofing them. There are also many locaters out there now.

I wrote a letter to my town mayor along with the explanation of the traffic danger he is not aware of, how busy the traffic is on the street and then a copy of paperwork showing his diagnosis. It took 2 months with 2 follow up emails but I got it done.

I just tried to get a "deaf child" sign for my street as my little one was recently diagnosed as hearing impaired on top of the ASD. Apparently in California at least, they are no longer permitted by state law. The town traffic engineer was really apologetic about it but he is required to follow state regulations.