What does it mean when people put a # in front of something?

[just_a_random_guy_asking_random_questions]

When someone writes something like #SWAG. What does the number sign mean?

[Me Gusta]

It means they add a word to describe the mood they are in, or a possible comment that they would like to add. On twitter it's called hashtag, and people use it to link tweets/make the hashtag a trending topic.

[A War on Life]

By definiton it means number.

[QJ]

It began on twitter you put the # to categorize it with trending topics now its used for emphasis. anytime you see the pund think POW then whatever follows

[Tom Carter]

The # (pound) sign is called a "hashtag". Hash tags are used by twitter community. They use it to add additional context and meta-data their tweets.