What does the flashing red light and key diagram on 2003 Buick rendezvous radio console mean?

The flashing red light and key symbol on a 2003 Buick Rendezvous radio console almost certainly indicates that the radio is locked due to an incorrect security code being entered. The radio's anti-theft system has been activated.

To unlock it, you'll need to find the correct radio security code. This code is usually tied to the vehicle's VIN (Vehicle Identification Number). You may need to contact a Buick dealership or a specialized car audio shop with your VIN to obtain the code. They might charge a small fee for this service.