Park off your employer's property, lock your gun inside a sturdy box attached to the car, and lock the car. That should be enough to thwart a smash and grab thief but won't help if he steals the car. To avoid attracting unwelcome attention, never mention guns at work.
Nebraska is an employment at will state. Unless you are a member of a protected class, you can be fired for any reason or no reason at all. Years ago, my supervisor was a private pilot. The CEO, after losing his son in a flying accident, went around to every pilot in the company and told them to give up flying. To keep his job, my boss parked his plane until the CEO retired. Another guy I knew worked for a computer service company. A few months after he was hired, the company insisted that he sign an agreement not to work in the same field if he left the company. He refused and was promptly fired. (He quickly found a better job with a competitor.)