Do you have "autism radar"?

Do you recognise signs in other people, that makes you think "they're guaranteed to be on the spectrum"?
I know one person that I am 100% certain is an aspie. 2-3 others that I strongly suspect. I would never tell it to their face, of course, but still.
(In all cases it has to do with mannerisms, use of language, "intense" interests)