This is an edit button.

[Bigboi]

It's pretty nifty. You can take a post you've already made, and make it something else, or even add to your previous post! Just click the button, and VIOLA, you're editing it! This will make double, triple, and even quadruple posts unnecessary.

 

[FuriousFox]

There's already a topic on this. http://ssntails.sepwich.com/mb/viewtopic.php?t=4621