In the "Quick Reply" box, you'll see an icon that looks like a globe with a link in front of it. Its right after the "A" where you can select different text colours.
Did you want it say "My Journal" or something like that, and have it highlighted as a link? If so, then write out whatever you want as the name of the link. For explanation's sake, I'll say you want it to be "Springflower's TTC Journal".
So write out Springflower's TTC Journal in your signature editor on BnB. Have your link that you want to put in your sig open in a different window. Copy the link from your journal, to go the signature editor and highlight "Springflower's TTC Journal". Click the Globe&link icon and it will prompt you to enter a link. Copypaste the link from your journal in there.
And you are done! Let me know if you have any problems.