there are some, but most are easily hidden.
the most visible signs are indeed posture and gait, but there are other differences, mainly in the skull.
i recently read "Morphological Features in Children with Autism Spectrum Disorders: A Matched Case–Control Study" which confirmed that there are indeed physical differences between ASD and NT people, it's available for free online, somewhere.
i myself have a rigid gait indeed, and if i'm getting stressed, my posture changes to a more natural feeling one; shoulders slouched forward, back arched forward, head protruding as well (so the entire spine in a continues curve instead of the 'normal' S-shape), combined with the stereotypical toe-walking.
i also have a more angled skull then most others, it isn't round per se, but appears to consist of straight plates with hard angles between them, and thicker parts on 'crucial' areas; for example, i have a more defined brow-bridge, some thicker bone lines over my temples, and a lumb where my neck connects to the base of the skull.