[quote=@thatguy]

The above image is the Department insignia tattooed on Operatives' necks. Operatives are plain clothes wearing agents. Your next door neighbor could be an agent and you would never know it.
[/quote]

Except for the tattoo on their neck?  It's not really something that a secret operative should have.  

Maybe if, we absolutely have to go with a tattoo, it's a UV tattoo that only shows up under blacklight?  That would actually be kind of interesting since the first scene is in a rave.  Because it would reveal the plot device, and allow the characters to work out how it works and what it means.