How to imply Ninja.

As previously mentioned, Iga is famous for Ninja. Problem is how to imply information of Ninja. During conversation with stranger, Iga-mono sometimes pick up word of Iga-Guri which means chestnuts and street vendor sometimes sell grilled chestnuts at festival. This matter sometimes turn out to be Ninja who are selling grilled chestnuts or when Ninja try to refer secret info. or Ninja relative matters. In order to confirm whether stranger is relative person or Ninja, Ninja ask question implying chestnuts in the conversation intentionally. And observe consequence of conversation spoken by stranger. In this sense, chestnut is secretive words or code when Ninja pick up topics. Iga-guri is usual Japanese word but only this chestnuts give hint to the person in reference with Ninja.