I've been trying to figure this out too, no luck.
I came across a huge list of macro commands that have it listed, but it doesn't even work for me.
/marking(/enemysign) [number (1-8)] [target] Set an enemy sign on the specified target. Select the type of sign using a number from 1 to 8.
(Set sign type 1 on target.)
^ this is the one that's supposed to work. if you use 'tab' on the chat window and go through the commands section.. u will eventually see "/marking" as one of the commands.. but as far as i know, it doesn't work. Edited, Sep 11th 2010 1:50pm by CEEREAL