What is this please...

[keyboard]

How and why would you use this ?

[Arantor]

This is the icon for RSS for the board; that link will give people the ability to get a list of new messages posted in that board.

Some people prefer to get news in RSS readers - Google Reader was for many years the goto tool, though Feedly is mostly its best replacement now. You take that link and give it to Feedly and it will show you the new posts as a sort of feed.