How do I get the little paragraph that's always there under my post?

[Aryetheral Waalburgus]

I've seen tons of users have a little paragraph about them that you can see under their post. It's in a gray font and separated from the normal post by a little gray bar. I'd like to make one, but I can't find where.

 

[casportpony]

I've seen tons of users have a little paragraph about them that you can see under their post. It's in a gray font and separated from the normal post by a little gray bar. I'd like to make one, but I can't find where.

Go here:
https://www.backyardchickens.com/account/signature