Where gill sans come from?

In 1882 Gill was born in Brighton
 Eric Gill, who had studied under Johnston at London’s Central School of Arts and Crafts,

 Edward Johnston. He was profoundly influenced by Johnston's

Gill Sans became popular when in 1929 Cecil Dandridge commissioned Eric Gill to produce Gill Sans to be used on the London and North Eastern Railway for a unique typeface for all the LNER's posters and publicity material.

The capital M from Gill Sans is based on the proportions of a square with the middle strokes meeting at the centre of that square. 

The Helvetica of England

http://idsgn.org/posts/know-your-type-gill-sans/
http://en.wikipedia.org/wiki/Gill_Sans
http://www.identifont.com/show?12W