While you may create an amenity in BrightSide for security cameras, Airbnb does not have a corresponding amenity to which you can map it. The amenity will show up on your website (if it is integrated and active) but it will not show up on Airbnb.
In order to notify Airbnb guests that you have a security camera, you need to login to your Airbnb account and go to Listings. In Listing Details, scroll down to Things guests should know and click Edit. Under Safety Devices, check the box for Security cameras/audio recording devices. Click Edit and describe each device, its location, and other details.