MonoBehaviour.OnMasterServerEvent  

function Start () {
    Network.InitializeServer(32, 25000);
}
    
function OnServerInitialized() {
    MasterServer.RegisterHost( "MyGameVer1.0.0_42"
        , "My Game Instance"
        , "This is a comment and place to store data");
}
    
function OnMasterServerEvent(msEvent: MasterServerEvent) {
    if (msEvent == MasterServerEvent.RegistrationSucceeded) {
        Debug.Log("Server registered");
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Start() {
        Network.InitializeServer(32, 25000);
    }
    void OnServerInitialized() {
        MasterServer.RegisterHost("MyGameVer1.0.0_42", "My Game Instance", "This is a comment and place to store data");
    }
    void OnMasterServerEvent(MasterServerEvent msEvent) {
        if (msEvent == MasterServerEvent.RegistrationSucceeded)
            Debug.Log("Server registered");
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Start():
        Network.InitializeServer(32, 25000)

    def OnServerInitialized():
        MasterServer.RegisterHost('MyGameVer1.0.0_42', 'My Game Instance', 'This is a comment and place to store data')

    def OnMasterServerEvent(msEvent as MasterServerEvent):
        if msEvent == MasterServerEvent.RegistrationSucceeded:
            Debug.Log('Server registered')