Sign off.
 
This saying came from a live action game that I ran, many years ago.  In it, spies with advanced technology plotted against one another, all competeing for a prize.

There were over fifty players, who recieved a dossier in the mail. It listed their "character", and gave them a target to "assassinate" within the rules of the game.

They never saw my face, only communicating through the mail, phone, or e-mail.  I ended every communication with this phrase.

To this day, I often use it with friends and family.