My mum, being well-meaning and I somewhat agree, suggested that I get an "I have autism" lanyard (or similar) for my son. He is 4. Non verbal. Still in nappies. He is happy and adorable but can be loud or do things which may not be the norm. It's at these points where she feels it might be worthwhile having one to alert people that he's not being naughty and me a shit parent but actually his behaviours are due to his condition/disability.
However, as much as I agree it would be helpful for people to magically know he is autistic, I hate the idea of doing it. I feel he is too young still. But I don't know. How would other people feel either seeing my son or if your son/daughter was disabled in the same or similar way. Ironically my son has an NHS staff style lanyard which currently goes everywhere with us but not worn. It's currently his favourite "toy".