If the Smart City Brake Support (SCBS) is operating, the indicator light (red) flashes.

Smart City Brake Support (SCBS)
Collision WarningMazda 6 Owners Manual: Cruise Control (Some models)
With cruise control, you can set and automatically maintain any speed of more
than about 25 km/h (16 mph).
WARNING
Do not use the cruise control under the following conditions: Using
the cruise control under the following conditions is dangerous and could result
in loss of vehicle control.
...
Mazda 6 Owners Manual: Direct Mode
Direct mode can be used for temporarily switching gears by operating the steering
shift switch while the vehicle is being driven with the selector lever in the D
range.
While in direct mode, the D and M indication illuminate and the gear position
in use is illuminated. Direct mode is canceled ...