on the square
1 honest; straightforward.
2 having membership of the Freemasons.
☞ A square, or more fully a set square, is an L-shaped tool for drawing angles, and together with a pair of compasses it forms one of the main symbols of Freemasonry.
❷1997Guardian One non-Masonic officer…claims he was moved sideways… and subsequently he discovered that the corrupt officers and the commander were all 'on the square'.