I found Heart (♥) and Broken Heart (💔) symbols in Music Hub of Windows Phone. Is there any relevance to these symbols in Windows Phone 8?
These are 'love' and 'hate' indicators. When playing a song you can tap on the heart icon (neutral by default) to switch between love, hate, and neutral.
These are used to provide you suggestions for other music in the Store and other related libraries. Possibly for Smart DJ too (though I don't have a reference for that).
http://www.windowsphone.com/en-US/How-to/wp7/music/music-and-video-faq # "How do I rate a song on my phone"