Great article on the history of Max Headroom.
It's a joke that's very specific to [Britain], I think. There is a huge firm that specializes in car parks, and [their] height restriction [notice] is "Max. Headroom, 6.5 feet," or whatever. From this single piece of signage, you had this title which everybody knew. As a consequence of [Max Headroom], national car parks spent about 3 million [pounds] changing all their signage to "maximum height".
Funny thing... the parking garage for my loft (here in the good ol' U S of A has a Max Headroom sign...
via The Verge