Is Autism an Invisible Disability?

It's said that autism is an 'invisible disability' because there isn't a distinctive autistic facial appearance, or some easily noticeable aid every (or most) autistics use, or whatever. However, it isn't always.
Firstly, some autistics present as very noticeably odd. Most people can probably tell someone is disabled if they are visibly stimming, have odd movement patterns and do not speak (with the exception of young children). Especially if, like many people who present that way, they have someone with them who is acting very patronizing and staff-like towards them. Some people describe this as 'looking retarded' which is probably what most people tend to think about someone who presents this way. If they can speak, but are doing so oddly, they may be considered retarded or 'crazy'.
Secondly, syndromal autism can be visible in the same way any syndrome is. Many conditions can cause both autism and a distinctive, unusual appearance. Some syndromes cause an appearance that isn't visibly odd, others cause one that is. I have a friend with a kind of syndromal autism, who has an unusual appearance and also walks oddly because of scoliosis and other motor issues. I think he's hypotonic, haven't been told this but he moves like a hypotonic person. Anyway, all those make it that, even if he acted fairly NT (which he doesn't) people would know he wasn't normal.
Lastly, if you know plenty of autistics, you can spot it even in 'mildly autistic' people. When I look at pictures taken of me when I didn't know my dad was taking a picture of me, my autistic mannerisms are fairly visible. The most obvious one, to me, is holding your arms up near your chest. CP people do this too, but it's different with CP - more stiff (I can recognize CP pretty well too). I just find that if I'm not thinking about my posture, very often my hands will be up near my upper body. This is only one example, there are others. It's like recognizing a person from a certain culture by their mannerisms (something I can't do, but lots of people I know can with cultures they are familiar with). My dad has noticed, for example, that Cree people sometimes point with their mouths.