Why is everything have stuff like "#________"?

[Cicero]

How come everything now seems to have the number sign (#)?

[Mortal Coil]

Hashtags, as they are known, were invented by twitter users. Each time someone posts a hashtag on twitter, it gets counted. If a certain tag gets posted a lot, it becomes something that's Trending on twitter.
They have since been adopted into the rest of the world, which is why you see them on bathroom walls, facebook and the like.

[Rayquaza]

Im sure you're talking about #hashtags

So basically, mostly used on twitter, rarely on facebook, these are like phrases which is always preceeded by a hashtag. When you hashtag something, it means that twitter will start adding that certain hashtag into it's database, and if that hastag starts becoming popular, it becomes trending. However, you don't have to use a hashtag to create a trending topic.

[TheMatrix]

#peoplewhodontknowinternetterms

[Steve Jobs]

#twitterwh0res. that's how it started.

[Aves]

Twitter.

[KidImage]

#GoodQuestion

[Steve Jobs]

That said, I've seen them used in barcodes too, lazy store managers who use excel to compile product databases and barcode numbers always use some kind of sign (hence # or ;) as a prefix to the number. Long story short, so the barcode scanners work with the product.

[TheMatrix]

That said, I've seen them used in barcodes too,
There is no such thing as a pound sign in a barcode, that doesn't fit there(you need 8 bits vs 4 bits).

lazy store managers who use excel to compile product databases and barcode numbers always use some kind of sign (hence # or ;) as a prefix to the number.
That's not lazy -- that's common practice. Putting "number" before each number gets redundant.