function OnDrawGizmosSelected () {
    // Draw a yellow sphere at the transform's position
    Gizmos.color = Color.yellow;
    Gizmos.DrawSphere (transform.position, 1);
}

using UnityEngine;
using System.Collections;

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

import UnityEngine
import System.Collections

class example(MonoBehaviour):

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