Historical Rules · 15 July 2011
Rule 206.3
Official source text from the 15 July 2011 Rules release
A guild icon appears in the text box of many Ravnica® block cards. These cards either have the specified guild's exclusive mechanic or somehow relate to the two colors associated with that guild. Guild icons have no effect on game play. Similarly, a faction icon appears in the text box of most Scars of MirrodinTM block cards. These faction icons have no effect on game play.