Request: Auto-appended comment to each post

Hi there.
While making tweaks to my site, I discovered a function I’d like to have, but haven’t seen anywhere. I did make a search of the forums, but didn’t find what I was looking for.
What I would like is to have a phrase or sentence attached to the end of each post.
I’ll explain my usage so it makes more sense in context.
I have a bulletin board on my web site, and I’d like to have a sentence at the bottom of posts that says something like:
“Discuss this on our Message Boards“.
A way to have the link changed based on the Category chosen would be cool, but I don’t know how possible that is.
I tried to just attach the sentence in my index.php file, but it doesn’t show up. Any ideas?