TexasCHLforum.com

The trick to remembering this is that the 30.06/30.07 laws only apply when you are carrying under the authority of your LTC. But since the LTC only applies when you are carrying against the normal law, it doesn't apply if you have a pistol concealed in your car in accordance with the law under section 46.02. Since it is not illegal to carry concealed in your car, even without an LTC, the signs will not apply to you.

But I concur with the other advice to never let your employer know you have the LTC or carry in your car. Anyone who went to that length (posting the parking lot) is probably fairly anti-gun and letting them know would be an example of a career limiting move.