I have used them with dd1 in the past.
we don't really anymore, as she is now a very tall 7 (nearly 8) year old, and so, imo, it is 'obvious' that she isn't just being naughty - and so lemon sucking members of the public can just piss off, quite frankly.
but when she was a bit younger (4 or 5) - when it looked like she 'should' have grown out of these behaviours, but clearly hadn't, we used to use t shirts at times like going through airports or similar.
her shirts usually said something like "i'm autistic, please be patient with me' or "I may n ot understand you if you talk to me" or similar. we found that by 5 ish, she was being addressed by people at check in, or security, and they were expecting her to answer (she did answer, but not usually what they were expecting
). it was just another flag (obviously dh and I would say somehting to secuirty, or cabin crew or whomever) to help ease our journey.
it also helped eg with people sitting next to her on the flight when they were trying to get past - since she clearly had a shirt on saying 'I may not understand you' then it was easier all round.
there are rpobably a couple of them that still fit, and I would not rule out using under similar circumstances in the future. because dd1 does not really display any challenging behaviours, it can be hard for people to get that she is not ignoring them, she just doesn't (necessarily) understand.