It's possible that a state statute may be violated by such an action but that would vary widely from state to state. Since a civilian is not subject to the UCMJ, violation of this base regulation has no legal penalty, it appears.
A military base is federal property, so I do not know how this would work out. If the civilian was carrying a weapon (Gun) which was legal in the state, but was not allowed when they entered the base.... Interesting.
I have contacted some of my friends who still work as Civilian Security/Law Enforcement on different bases and asked them if they could point out specific cases.
When I hear back, I will let you know.
When I was on active duty, I was involved in an incident on base with a civilian friend. I eventually received a letter of counseling and my friend received a Magistrates ticket.
When we went to court, my friend was told he could face up to one year in a federal prison if convicted. Charges where dismissed.