[Users] $an tag appears in all my email headers

[Cliff Laine]

Afternoon,

Does anyone know why a $an tag is appearing, against a pale yellow
background strip, as the first header in the message view?

Here's what it looks like
http://imgur.com/a/b891E

I'm using CM 3.13.2 in Lubuntu (Ubuntu 16.04.1)

Thanks 

Cliff