The Security Guard is a new Legendary card that can be found in the main park. The Life Guard is the Water Park equivalent of the Security Guard. They are Utility buildings that can be found in the Service section of the Attractions Build menu.
Both buildings will produce Appreciation Hearts over time. To maximize their production, make sure to level up the cards and to have a good park coverage by placing them in strategic positions. They will also produce more if the park's Overall satisfaction is already high.
To collect Hearts, simply tap on the building once the "Collect" bubble appears. Hearts will be generated even when you are offline.