I found this looking for insulators behind some old buildings, and was searching through a metal bin, and found this, as well as a lag screw insulator possibly off ofa nearby building. On the top it is embossed DL&W as well as another mark looking like a capital N.

UPDATE: 9/9/08: This has been confirmed as a railroad lock, and has an estimated value of $30.00, and would be around $50.00 if in better condition. Thank you to all who contributed any information regarding this item.