The "writing under your name" is what we call a "Custom Title", and it's something the mods give you if and when they feel like it. I went to Ireland eight years ago and it's stuck with me ever since.
The text that appears beneath your posts is a Signature, and can be edited from within your Profile. The profile link looks like this
and is in the top-right corner.
Once you're in there, look on the left for something like this:
That's where you can change your signature. Note that this forum does not allow signatures with images, or that take up more than two lines.
