My company is rolling out SP 2013 for the corporate intranet.  At the top of the site structure, we have "root" site collection.  Call it "Main".

 Because of the structure of our organization, the way our heiarchy is one where underneath Main are several site collections on a managed path, so what it looks like is this:

http://main
http://main/sites/site1
http://main/sites/site2

etc. where site1 and site2 are actually site collections and might have a number of sites below them.

What I want to have happen is to change the link in the logo image so that no matter where you are in the heirarchy, you will go back to Main.  I know I have to edit the masterpage to do this, and I'm comfortable editing the master page, but which tags do I edit?

One way is to change masterpage and add your own logo with hardcode link to the root site. Think, there is no sharepoint out-of-the-box behavior for this...