Excise and Licenses will email a professional license to all security guards. This license (or a clear picture of the professional license) must be carried by the security guard at all times during which the security guard is working.
The permanent security guard badge issued by Excise and Licenses must be worn on the outermost part of their uniform or clothing in a clearly visible manner at all times during which the security guard is working. If a badge is lost or damaged, a replacement badge can be requested online.
He would have to had several additional endorsements, along with a specific permit to that event, to be traipsing around in plain clothes with a firearm.
According to the Denver licensing website:
No visible identification is illegal.
All guidelines for security in Denver:
https://www.denvergov.org/content/dam/denvergov/Portals/723/documents/Rules%20Governing%20Security%20Guards%20and%20Private%20Security%20Employers.pdf
He would have to had several additional endorsements, along with a specific permit to that event, to be traipsing around in plain clothes with a firearm.
My guess is he has none of these.