Below is the dirt from their blog.
Quick tip - One of the best-kept secrets of Snap is that you can add
your logo for free! It’ll show up whenever your listing shows up on
Snap. The path to get to free is a bit obscure (do a search, then look
for “Your site, logo or offer here” in the upper left. Then click and
read.) Oh, what the heck, just click here.

http://www.snap.com/wordpress/index.php?p=23