An Echo is an alert that happens when two members have shown mutual interest in each other.
Where do I find Echo's?
Likes you receive will be labeled with ECHO! when someone you sent a Like to sends one back. Messages are labeled with ECHO! when someone you sent a message to replies for the first time.
If you are logged into the site, echo's will appear as Onsite Notifications anytime a member responds to you liking or commenting on one of their photos.