Postal is a scrapped vehicle from Twisted Metal III. It was shown in videos of a very early prototype build of the game by PlayStation Museum.[1] [2]
According to Jim Buck (the game's main software engineer), lawyers weren't happy with the game including a USPS van, so they had to cut it. It was scrapped before any character, story or special weapon were ever created for it.
Design[]
It was a white USPS mail van based on a Grumman LLV truck, with machine guns strapped on the sides of its roof and a pot lid mirror on the right side of its hood.