Flinches if surprised, picks at skin or scratches more than normal (there might be visible sores from this), intense preoccupation with things ordinarily beneath interest, hard to interrupt from work, drinks lots of water if responsible, particularly unconcerned with thirst if not. Particularly prone to discuss subjects at length, perhaps an unusually quiet or loud vocal tone.

There's also of course the side effect list, which usually reflects this sort of thing: https://www.drugs.com/sfx/amphetamine-side-effects.html