A comment on an old AR Unity application I did asked the following question: "Hi I want to control one object using two markers. For ex. When both the marker is visible than cube has blue color and when one marker is visible cube will have red color. How to use onmarkerfound, onmarkerlost eventrecievers in such a case?" This example answers that question using ARToolkit.
This example is currently built using Unity 5.5.0f3 This example is currently built using ARToolkit Unity Plugin ARUnity5-5.3.2.unitypackage. If you don't need the entire project and you already have a project using ARToolKit, just grab the Unity Package File It's located under the 'Assets/Unity Package' folder. Take that and import it into Unity3d using the normal unity3d import package options for custom packages.