Why do people put a pound sign after their posts on social networks?

[Jamaican QTâ„¢]

I don't have twitter, and I don't use myspace, but I've noticed that on facebook, people have started using the pound sign (#) a lot in their posts. Is there some meaning behind this, and did this start on some other social networking site?

Here's an example of what I'm talking about, "I hate when cops pull you over for a rolling stop #peeved."

I tend to just say, "I'm peeved about (insert whatever here)."

Someone fill me in on how this trend started and why...

[Nonya]

It's how you "tag" things so that you can just go look at what other people have tagged, it started on Twitter. It doesn't function on Facebook like it does on Twitter but here's how it works.

I'm tweeting "Charlie Sheen #winning" you could click #winning and see what other people were talking about when they tagged winning. Does that make sense?

My brother does it a lot, I think it's #stupid unless it's actually on Twitter.