Wouldn't be the sickest prank I've ever seen in the army
But the house "near the entrance to Ft. Hood", where the pickup truck was parked, was two miles from the gate and in a civillian neighborhood. The guy who owned the pickup, AFAIK, was not active duty or veteran - but the guy who first saw it spent a lot of time telling everybody he sure as shootin' was a veteran.
Personally, I think the device was a warning from the Vietnamese or Cambodian Mafia - a warning to some guy who took "all you can eat shrimp" beyond the limits at a buffet.
stay safe.