A particularly 'observant' child, he noticed even the slightest changes in the classroom.
an 'observant' Jew/Muslim = a Jew/Muslim who is 'observant' of Jewish/Islamic law
Good reporters are keenly 'observant' of everything around them.
(..) Where'd they go? Is it hard to get to be in the Secret Service? Why? I was just curious, 'cause I think I'd be good at it. I'm very observant. I was in the Marine Corps. I'm good with crowds. I notice there's a little pin there. That's like a signal, isn't it? - Sort of. (..)1976 Taxi Driver