IMO it is almost impossible to get the bindings too far forward on most recreational system bindings as the plates are set too far back to begin with. The delta angle of the binding also is just as important.
Hints for too much delta and/or too far back: The ski skids too easily. You never feel the entire ski underfoot, just pressure on the heel area in the boot. Your butt and hips easily stick out the back of the skis and people riding the lift yell out to you asking if you want any toilet paper. You find you have to mash the cuffs and constantly be applying serious forward leverage on the boot cuff to get any tip pressure, otherwise the tails wash out when set on edge. You tire quickly as a lot of unneeded movements and energy is expended to stay forward, or you think feeling the front of the ski is someplace you should never be and just give in and ride the tails and never advance.
Hints for being too far forward or not enough delta for your anatomy/setup: You find it difficult remaining balanced in turn transitions and find it difficult to exit a turn. You have the sensation of going over the handlebars if you apply any cuff pressure. You feel more balanced with your hands at our side or behind you. The skis feel like they are nailed to the snow and won't initiate a turn without gross movements. You have to throw your hips way back when breaking or scrubbing speed.