Copy/pasted from the FAQ page:

"For members who are open to dating, you will see that SOME thumbnails and profiles have a heart symbol on them with a percentage. This helps you identify which members are open to dating as the percent shows approximately how compatible you are with them. If you click the heart symbol on the top of their profile, you can see how it is determined.
You can improve your score in general by answering all the profile questions and writing a bio."

Compatability if you are dating.

For a sweet thought may have been made or a little support given?