If you watch carefully, the Messaging Tile on Windows Phone 7 will change as you receive messages. When you receive a new text, you’ll hear a sound and a brief notification will appear at the top of the screen. Additionally, when you have new text messages, the Messaging Tile on the Start screen will show you how many you have and the emoticon on the Tile will change.
The emoticon smiles at you when you don't have any new messages but the smile becomes a wink once you receive a new message. When you have four or more messages, the emoticon will change again.