Another approach would be to add a thumbnail to each of your six templates and call the thumbnail image. That would give you flexibility if you add templates or change your icons down the road.
To add a thumbnail, go to Page Templates --> your template --> General tab --> Thumbnail [image] --> upload.
Then the transformation can grab the thumbnail image like so--
<img src="~/CMSPages/GetMetaFile.aspx?fileguid={% DocumentContext.CurrentDocument.DocumentNode.Children.All[0].NodeTemplate.Thumbnail.GUID |(identity)GlobalAdministrator%}"/>
And in case you haven't found it yet, one of my faves is the handy macro utility under System --> Macros --> Console that can help build and test macros (with real or virtual data).
Good luck!