The concept of Enforcers was created by Mayor Jane Derren, a hard-line Conservative Unionist and San Paro's youngest ever mayor. It was codified in the CSA (the City Security Act) that she put in place. You can read all thirty-six pages of this momentous document down at City Hall - enshrined in an armored glass case - but what it boils down to is that licensed civilians have the right to bear arms and to act as vigilantes in support of the law.
Like the other recruits, you are as likely to have come from the military or law enforcement as from the general citizenry. You aren't a cop: you are part of a movement that has been collectively dubbed 'Enforcement'. After rigorous training, you now work with one of several groups who receive information and dispatches from the CSA facility in Fourche Bank - organizations like the Prentiss Tigers, or the Praetorians. They'll provide your assignments, coordinating their execution through the city-wide Dispatch Net.
You respond to flash points or crimes in progress, and complete vital Enforcer operations, keeping the city under tight control. Rewards are paid automatically. Vehicles, weapons and equipment are at your disposal, but as a private citizen, these must be purchased from your own funds. How you choose to look is your own affair. At all times, you must be ready to use lethal or non-lethal force against Criminal insurgents, as authorized in the terms of your license.
Your authority comes straight from the Mayor herself.
San Paro is at war. Protect your city.