If there is a 'tag' written in black under a persons ID name, they put it there themselves. After you have been registered for 30 days and have posted 30 or more times, in your User CP a new option appears (following the place where you put in your birthday) and you can write your own tag. Only Tag Faries can write in color....and NEVER attempt your own tag AFTER the Faries have tagged you....or you will erease the ones they bestowed upon you. On the Community Board you will see a thread from members of the Tagliarchy, a group of DISers who attempt to attract the Tag Faries on behalf of the tagless. Offers of chocolate, cash and lots of clapping help attract the Tag Faries. And members of the Tagliarchy also hold objects of power (we have a rich fantasy life) to aid them. If you stop by and post a message, they will work on your behalf. It worked for me I got a triple hit!
Good luck from the recently inducted keeper of the official Tag Fairytale Storybook!