When the connection to the XMPP server is secure/encrypted, Spark displays a little lock symbol in the botter-right corner of the contact list. When the connection is not secure, nothing is displayed. This could lead to situations where people assume encryption is in place, but have no visual indication that that's not the case. If a user does not know that a lock is supposed to be displayed, the user won't notice.
Spark should display a symbol (a lock with a red cross in it, something like that) when the connection is not secured.
So I went with an 'unlock' icon that was already in Spark. Feel free to add a better icon though