function OnGUI() {
    if (Network.isServer)
        GUILayout.Label("Running as a server");
    else if (Network.isClient)
        GUILayout.Label("Running as a client");
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnGUI() {
        if (Network.isServer)
            GUILayout.Label("Running as a server");
        else
            if (Network.isClient)
                GUILayout.Label("Running as a client");
            
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnGUI():
        if Network.isServer:
            GUILayout.Label('Running as a server')
        elif Network.isClient:
            GUILayout.Label('Running as a client')