The bottoms of your horse's feet will start to look robust and durable. The soles will be thick and hard. The bars will be pronounced and strong and the frogs will look quite solid and tough. There may be some chipping around the edges of the wall. This is normal.
Mother nature trims feet by breaking or wearing off the excess.
The signs that barefoot isn't going to work are pretty easy to spot. Your horse will be way more than a bit sore. He may be anywhere from quite uncomfortable to downright lame. His feet will get hot and his legs may fill slightly. He might break big chunks out of his feet or they may look like they are disintegrating.