Historical Rules · 27 September 2013
Rule 207.3
Official source text from the 27 September 2013 Rules release
A guild icon appears in the text box of many _Ravnica_ (R) and _Return to Ravnica_ (TM) 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 Mirrodin_ (TM) block cards. These faction icons have no effect on game play.