What does this icon do?

[pseudoSequential]

The icon/button I am talking about is located in the upper right of the screen when in flight, and the bottom left of the screen when building. It resembles a wireless icon, and has a little 0 under it, and when moused over it says none.

Please help, I am deadly curious and have not been able to find an answer! Thanks!

[DeMatt]

You mean this icon?

If you complete a contract (or perform some other actions that give you messages), KSP puts a message to that effect under this button. It simply says "0" and "none" because there's no messages to display. Obviously, you need to be in a Career-mode game to get contracts.

For reference, the other three buttons from left to right are:

1. Money/Reputation/Science counters
   
2. Shipboard resource display
   
3. Contract requirements listing
   

[Volcanix]

You mean this icon?

http://i.imgur.com/MqRM61F.png

If you complete a contract (or perform some other actions that give you messages), KSP puts a message to that effect under this button. It simply says "0" and "none" because there's no messages to display. Obviously, you need to be in a Career-mode game to get contracts.

For reference, the other three buttons from left to right are:

1. Money/Reputation/Science counters
   
2. Shipboard resource display
   
3. Contract requirements listing
   

What other action gives you a message? Have I missed something from KSP? I thought it would only give you a message when you finished a contract.

[ElWanderer]

Rescuing a Kerbal triggers a message to tell you they've joined your space program. That's tied in with contracts, mind.

In future, there could be other messages to alert the player in there.

[SRV Ron]

It flashes green for a few seconds when a contract is completed. The number zero changes to reflect the number of completed contract. So, if you have completed 12 contracts, the number 12 would be displayed there.

[Taki117]

What other action gives you a message? Have I missed something from KSP? I thought it would only give you a message when you finished a contract.

It will also display if you have completed a part of an "Explore" contract, or if you have a Debris Recovery mod those will also give a message. Kerbal Construction Time will also notify you of Vessel Completion.