Like the other answer mentioned, Behold the Coagula is the cult ran by the Armitage family where black people bodies were transplanted with white brains, such that they could join the black superior physique with the white superior intellect.
The blue insignia at the bottom was the symbol of the Order. I'm not sure it has any specific meaning attached to it.
For completeness' sake, I'm also quoting the Wiki:
Headed by the Armitage Family themselves, members of this unusual secret society seek out, kidnap, brainwash, and finally "trade places" with healthy and youthful Afro-Americans via [partial] "transmutation" which is to implant the brains of the members, their old relatives and friends, into the bodies of the far younger and fitter black people.