Right, I've been working on http://www.youtube.com/watch?v=SO-OMWk0mQs&feature=youtu.be&hd=1 vid. I get to where I double click on my new cell but I don't see the red markers as shown in the vid. The data's in the right hand screen as shown in the vid, but there's no visual markers on the render window.

Press the M key and see what happens.