DO NOT DO THIS EVER!
This is a HUGE HUGE no-no at Assateague Island, do NOT pet the horses. Aside from the fact that they're wild animals and may retaliate (this one almost did), they need to be wary of humans. This photo was one of several that I turned over to the park rangers, and while these folks left the park before the rangers arrived, a file was opened. Seriously, do not do this, you can be fined and arrested, and it's bad for the horses.