You can use standard HTML to insert an anchor to the text:
<span id="myHeading">My heading</span>
======================================
and then link to it like this:
[My heading](./#myHeading)
If you have the wireframes in your git repository, the best solution is to use the "raw" links in the gitweb viewer for your URLs, e.g. http://exampleproject.git.sourceforge.net/git/gitweb.cgi?p=exampleproject/projdir;a=blob_plain;f=wireframe1234.png;hb=HEAD - you can get these URLs by selecting Code > Git Browse from the SourceForge project page, then clicking on "tree" and finally copying the link URL from the "raw" link next to the wireframe file you want.
If your project is not using git, another solution is to upload the image file to the Files area of your SourceForge project.
You should do this in a sub-folder, to avoid cluttering the Files page with all sorts of things that most people will not want to download. After creating a "wireframes" folder using the "Add Folder" button, and uploading your wireframe images, refresh the page and then click on the link, which takes you to a download mirror page. Copy the "direct link" in the header - this will be a URL like https://downloads.sourceforge.net/project/exampleproject/wireframes/wireframe1234.png?r=&ts=1326447090&use_mirror=voxel and use this as the URL for the image in your wiki.
Disadvantages of the "Files" approach are that you will need to re-upload every time you have a changed wireframe, and after you do that, SourceForge will suggest "Looking for the latest version? Download wireframe1234.png (17.2 kB)" at the top of the Files page to everyone. Also, if the SourceForge mirror site stops mirroring, you would need to update all the &use_mirror=xxx in the URLs (this is not very likely, though).
Best Answer
Just hover on the "Mailing Lists" button to see the menu, and select "Search Mail Lists" option. Now you can use the "Advanced Search" page to run your query.