This isn't exactly true.
SECTION 16-23-20. Unlawful carrying of handgun; exceptions.
It is unlawful for anyone to carry about the person any handgun, whether concealed or not, except as follows, unless otherwise specifically prohibited by law:
(9) a person in a vehicle if the handgun is secured in a closed glove compartment, closed console, closed trunk, or in a closed container secured by an integral fastener and transported in the luggage compartment of the vehicle; however, this item is not violated if the glove compartment, console, or trunk is opened in the presence of a law enforcement officer for the sole purpose of retrieving a driver’s license, registration, or proof of insurance;
Also, per the law, any business who wants to prevent patron or employee concealed weapons carry must post a sign at every entrance point and it must be a sign in compliance with the law, not just some cardboard taped to a window saying "no gunz aloud".
Of course if you work on federal property, their rules trump these. For everything else, you're allowed to retain your firearm in your vehicle.