public var showOnTop:boolean = true; // banner on top or bottom of screen
public var dontDestroy:boolean = false; // keep this GameObject around for next scene

// don't make this a local variable, or else it'll get garbage collected
private var banner:ADBannerView;

function Start () {
if (dontDestroy) {
GameObject.DontDestroyOnLoad(gameObject); // keep ad alive if we load a new scene
}
Debug.Log("Creating iAd banner");
banner = new ADBannerView(ADBannerView.Type.Banner,showOnTop ?
ADBannerView.Layout.Top : ADBannerView.Layout.Bottom);
ADBannerView.onBannerWasLoaded  += OnBannerLoaded;
}

function OnBannerLoaded() {
Debug.Log("Ad banner Loaded!\n");
banner.visible = true;
}

? From:http://www.fugutalk.com/?p=6387
官方C#:https://docs.unity3d.com/Documentation/ScriptReference/ADBannerView.html