I can't give a general answer that an expert might provide, but I can give you my own sense of things as I've been working through just this lately. So a few thoughts:
First, I'd say that the better I get at NOT flipping it, the better I am at being able to tell when I do flip it. So in some sense I know it's a leakage hook if I can tell I'm flipping it. But that's the obvious answer and is probably unhelpful.
All other things equal (i.e. the ball draws in either case), I'd say the following:
With leakage the ball tends to:
- start further left
- go higher
- go shorter
3. Without leakage the ball tends to:
- start right of target line and then come back to the left (because the draw isn't caused by flipping the clubhead but by hitting the ball with a clubface that is closed relatively to the path)
- start with a much lower trajectory
- go much further
So, I'm sure this isn't a hard and fast rule, but for me, if I start the ball right and hit it on a low piercing trajectory with a slight draw, it's a completely different shot then when I flip at it and hit the ball left to left on a higher, weaker trajectory.