It could be "N(x) H(x) Police", but I'll bet on Nevada Highway Patrol. "HP" usually means "highway patrol" and of the two states beginning with "N", only Nevada uses that designation (Nebraska uses "State Patrol"). "New Hampshire Police" and "New Hampshire Patrol" are not valid terms, and a two-word state (New xx or North xx) would use both initials.
(Old Fuff, I know what you mean. I saw a post the other day asking about an old revolver from 1976!!)
Jim