Appears to be a reference to British rule, especially military occupation.

Example from Lord Henry Cavendish-Bentinck (Conservative) in a British parliamentary speech, 1914: "The crime that is existing in Ireland now is the result of Ireland being governed by red hats, by tanks, and by men in steel helmets. If you remove the tanks, the red hats and the steel helmets, and give Ireland the opportunity of governing itself, crime in Ireland will die away at once."

Signed this time (I hope).