The feet will be hot, and you will able to feel pulses (talk to your vet or farrier about how to feel for these). The horse will also take a stance with their front legs far out infront of them to reduce pressure on the painful areas of their front feet. In less advanced cases the horse will only be lame infront, however the pulses will always be there (these are the best indicator).
Immediately call the vet, bute the horse, get him standing in ice water or cold hose and standing on soft surfaces and/or tape thick styrofoam to the bottom of his hooves after icing them.
They say money doesn't buy happiness -- well happiness doesn't buy horses!