I guess you're new to Yahoo messenger.
Maybe, that was his avatar picture in the form of a star. Whatever avatar your contact chooses , appears before the left of the name.
You can choose your avatar as well.
1. Just open Yahoo Messenger.
2. Press
Ctrl+Shift+K or go to Messenger Menu->My Display Image
3. Choose Share my picture and click
Select...
4. In the window that opens, choose one of the pictures available or click
Browse.. to choose your own.
Alternatively, you can create your avatar by clicking on Create Avatar in the first window.