I keep seeing this symbol appearing more and more on TV etc. " # " what is it supposed to mean?

[palekna]

I know it's a number sign, a tic tac toe and a lbs sign. What is it's newer meaning?

[J]

It's a hashtag. It's used a lot in social media, especially on twitter and instagram (tv shows can have official accounts on there). It can be used to find tweets on twitter or photos on instragram that have words in common. For example, if someone is looking at the hashtag "#beach" then they would see lots of photos and tweets about the beach.

[Nelson]

It is either a hash tag or a designation for 'number of' something.
EG # girl, Mary, audience are three ways to find a name on social networks (hash tag)
OR
What # of people are you bringing to the picnic.