The guy with the "Blacks for Trump 2020" sign at the President's Phoenix rally is an ex-cult member ... who was once charged with conspiring in 2 murders.

Maurice Symonette was once a member of the Yahweh ben Yahweh cult, led by preacher, Hulon Mitchell Jr. -- who was federally charged in 1990 with conspiracy in multiple killings, one of which included a beheading in the Everglades. 

Symonette himself -- as well as at least 10 other cult members -- was charged in the '90s for allegedly conspiring to commit 2 murders ... this after his brother told jurors Michael helped beat one man and jammed a stick into another guy's eye. 

He was later found not guilty.

As we told you ... Symonette runs a website that's pretty out there -- accusing "ISIS & HILLARY RACE WAR PLOT TO KILL ALL BLACK & WHITE WOMEN OF AMERICA" ... among other racially charged allegations. 

Apparently, Blacksfortrump2020.com was just the tip of the iceberg for this dude. Good placement, team Trump.