See Controls and Indicators → Instruments → Instruments: FLHTCUTG. The security lamp in the speedometer face indicates the status of the security system.

Armed: A lamp that blinks approximately every three seconds indicates that the system is armed.
Disarmed: After the system disarms and the ignition is on, the lamp will remain illuminated for approximately four seconds and then turn off.
Service: A lamp that remains illuminated longer than four seconds when the system is disarmed indicates that service of the module is required.