Scripting Reference
Gizmos.DrawGUITexture

static function DrawGUITexture (screenRect : Rect, texture : Texture, mat : Material = null) : void

static function DrawGUITexture (screenRect : Rect, texture : Texture, leftBorder : int, rightBorder : int, topBorder : int, bottomBorder : int, mat : Material = null) : void

Description

Draw a texture in screen coordinates. Useful for GUI backgrounds.

JavaScript 
var myTexture : Texture;

function OnDrawGizmos () {
     Gizmos.DrawGUITexture(Rect(10, 10, 20, 20), myTexture);
}
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Texture myTexture;
    void OnDrawGizmos() {
        Gizmos.DrawGUITexture(new Rect(10, 10, 20, 20), myTexture);
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public myTexture as Texture

    def OnDrawGizmos():
        Gizmos.DrawGUITexture(Rect(10, 10, 20, 20), myTexture)