Security guards are required to be licensed in most states. They must go through a state-certified training program prior to being certified and are required to carry their licenses at all times when working. Checking to see if a guard is properly licensed is a simple process if the guard is cooperative. If he is not, he likely does not have a license or is not carrying it as required by law.
Ask to see the guard's security license and driver's license. He should have both on him if he is working in a legal capacity.
Check the name on the driver's license to verify that it matches the name on the security license.
Examine the security license. Every state license looks different but there should be a license number specific to that particular officer, the name of the agency that issued the license and an expiration date. Check the expiration date to make sure the license hasn't expired.
Check the website for the agency that issued the guard's license. Many states, such as California, allow you to check a guard's license status online by entering the guard's name or license number.