When it comes to "flexible" rules such as "yield on a green light to oncoming traffic", drivers can be forgetful. A sign is a helpful reminder.
Standard: 01 The CROSSWALK STOP ON RED (symbolic circular red) (R10-23) sign shall only be used in conjunction with pedestrian hybrid beacons (see Section 4F.02). 02 The EMERGENCY SIGNAL (R10-13) sign shall be used in conjunction with emergency-vehicle traffic control signals (see Section 4G.02). 03 The EMERGENCY SIGNAL—STOP ON FLASHING RED (R10-14 or R10-14a) sign shall be used in conjunction with emergency-vehicle hybrid beacons (see Section 4G.04).