Click on the "Thread Tools", then "Edit Thread". In the pop-up which appears, you'll see a "prefix" option in front of the thread title with a drop-down arrow. Click that and choose the prefix you want.
You'll see a similar option next to the thread title when creating new threads in forums which support prefixes.
Click on the "Thread Tools", then "Edit Thread". In the pop-up which appears, you'll see a "prefix" option in front of the thread title with a drop-down arrow. Click that and choose the prefix you want.
You'll see a similar option next to the thread title when creating new threads in forums which support prefixes.