Hi jmb,
Have a look at the original post - it has a nice picture and everything.
http://www.iceinspace.com.au/forum/s...8&page=2&pp=20
The red light pen can be used to take notes at the telescope (or binoculars). You can record what you see and the red light does not spoil your dark adaption ie you aren't blinded when you look into your eyepiece or binoculars.
Very handy if you are going to record your observations in a log book.
Adam