Turns out the screen on my Powerbook is so thin, that a bit of sunlight on it’s back will make my screen look like this:

This is the Apple logo on the back of my laptop shining through to the front of the screen. The logos used to have their own lights in the days of old, but now they are lit via the LCD backlight, thus leaving a bit of a light hole in the LCD backing. Quite annoying, but nothing a strip of gaffa tape didn’t fix : )