Ten years ago today, Twitter introduced the hashtag, aka the pound sign. Hashtags were designed to help organize Tweets of similar subjects and while many people do use it that way, most have taken the symbol to a whole new (and often overused) level.

Facebook incorporated hashtags a few years ago and soon users were hashtagging entire sentences. Now, you can pretty much use them on any sort of social media platform and they work the same way there as Twitter intended them too.

So what are the most popular hashtags? The Indy Star reports that #NowPlaying has been tweeted more than a billion times and #FollowFriday is a close second. Other popular hashtags include #TheWalkingDead (for TV), #StarWars (for movies), #NFL (for sports) and #SuperBowl (for sporting events).

A few years ago Twitter started adding fun graphics at the end of hashtags and today is no exception – if you use #Hashtag10 on Twitter, a special graphic with a balloon will appear at the end of the 10.

For more on how to use hashtags, check out this helpful guide from Mashable.