I usually look for stumbling or one of the legs moving slower or more awkwardly than the others. If your on the horse and feel that your rocking too much or the horse feels unbalanced ask a friend to check if they’re lame. If you feel the horse’s leg and it is really warm or hot then your horse is probably lame and you should then look for the cause. Sometime the cause is over work, other times it and be more serious. If you still don’t know what the cause is after you thoroughly checked it call your vet.
Hope this helps!
There's loads of signs. Sometimes they're subtle, sometimes obvious. Sometimes they're from excitement/energy, sometimes pain. Sometimes it's just conformation and breed. It's more a combination to look out for, that any specific sign.
-Reluctance to move forward
-An uneven step/ a leg spending too long in the air
-Head bobbing when it shouldn't (trot)
-Tension in the eyes
-Tension through the body
-Sometimes when you can't see a bad step, you can hear it so close your eyes and have someone trot the horse on a hard surface
-A horse that's lame on a soft surface but not a hard one would tell you that it's soft tissue damage
-A horse that's lame on a hard surface but not a soft one would tell you that it's bone/joint damage (they can be lame on both though)
-Seems stuck at a certain point
-Will not let you touch a certain point, or is sensitive there
Every horse is different though, and it's only really through watching gaits that you learn to see.