On Facebook what does it mean when someone posts The @ or # sign before someones or somethings name?

[Ben]

It means they're mirroring their twitter feed. You can set it up so that any twitter updates are automatically set to your Facebook status. The @ is used to direct a message at someone. That will work in Facebook now to- just type @name in your status. The person you tag will be notified and the status will link to their page. The # is a twitter hash tag. One of the things you can do on Twitter is search for what other people are saying about a topic. But because there are so many tweets every day, any query will turn up a lot of bad results. By putting the # sign in front of a word, you're saying that this is the topic of the tweet, so that it can be found in a search easily.