This clicker called a Memphis Cricket and is one of various different styles of clickers used during the Normandy D-Day attacks.We did not realize that there were many different types of crickets used in the D-Day airborne invasion by the 82 Airborne and 101^st Airborne. 

We got this one from a guy who had a few on eBay 20 years ago, sold from his military antique store in Covington Kentucky .

The “click-clack” of the cricket helped the soldiers of the Airborne Division communicate with each other without alerting the German troops. Used for communication to distinguish friend from foe. When approaching an unknown person, one click would be made using the tool and friendly troops would respond with two clicks.