It's normally pretty simple to see, as dannyra said. A block will go straight through the air but to the right of the target. It doesn't have any sidespin on it so that the ball contibues in the direction it was hit.
A push-slice will start right of the target and then curve through the air from left to right (for a right handed golfer) as it has lots of spin spin on it.

Have a look at this page http://www.tydaniels.com/hook-slice-fade/