When you make a post like here: LINK, there is a section near the bottom that reads TAGS. Just type in your characters name and a comma and the name of another character that is in the thread with you. If you're just starting a thread then you just type in your own character name. The purpose of tags is for pure searchability, not for letting others you want them to join them in a post. If you want a character to join you in a post then contact the player either by AIM, Email, Private Message or just post a note on trapped_ooc.
When you join a thread that has already started you can edit the tags to that thread to add your own character tag to it as well, as seen here: LINK
But don't worry too much about it. As a mod, I make a point of checking posts for tags and if they're not there I will add them myself. If you have any other questions about this or anything else, please let me know.
- Trapped Mod
{P.S- Sorry about the wrong journal. I forgot to log out as Patrick}