function OnDrawGizmosSelected () {
    // Draw a yellow cube at the transforms position
    Gizmos.color = Color.yellow;
    Gizmos.DrawWireCube (transform.position, Vector3 (1,1,1));
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnDrawGizmosSelected() {
        Gizmos.color = Color.yellow;
        Gizmos.DrawWireCube(transform.position, new Vector3(1, 1, 1));
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnDrawGizmosSelected():
        Gizmos.color = Color.yellow
        Gizmos.DrawWireCube(transform.position, Vector3(1, 1, 1))