Quick Answer:  Early signs of Laminitis:
1.  Crest beginning to feel fuller
2.  Putting on weight 
3.  Check pulses, should hardly be able to feel any   
4.  Typical laminitis stance, weight back on hind feet, front feet reaching out to take the weight off them. 
No. 4 is a VET EMERCENCY call your vet now.

Laminitis is very painful for the horse and can last for a long time.  Vets often recommend a perion of box rest where the horse is kept in a stable 24/7.   However opinions are beginning to change and many vets now prefer the horse is in a very small dry lot where he can move around if he wants to.

The footing for this kind of pen is very important, sand or sawdust is soft on those painful feet. Straw or chippings not so good.  Soft hay will do as well.

Watch for any of the early signs of laminitis above, keep your horse slim even if you have to use a grazing muzzle (choose a soft one like the LiteBite)  any restriction you can place on grazing will help keep your horse safe.

Be vigilant and if anyone says "he's put on weight"  take note, laminitis once had can reoccur very easily and you have a lifetime of worry.