HTML Link from home page to sub page

Quick question.

I am making a default theme and layout that will be cloned when a new member signs up. I am putting in default forms, images, posts, etc.

In the widgeted sidebar, I have an image that links to one of my pages where there is a lead gen form. When the site is cloned, the I don’t want the image to link to http://SITEONE.com/subpage, I want it to go to http://SITETWO.com/subpage.

So, in the HTML I put Untitled Link<img class=”a…………………..etc.

This works, but only if they are on the homepage. If you click the sidebar on a subpage, it tries to link to http:SITETWO/subpage/subpage and doesn’t work.

How do I code this link so it pulls from the home page url all the time rather than from the page the person is on.

Hope this makes sense. I confused myself.