Turns out that, according to these lists I am pretty unwell read. I scored better on the British list. The American lists were weird. Save the image and fill in your own if you like, I am generously hosting my own list and a blank one on my famed (ha) website.
Comply with Red X. These signs feature on the overhead gantry on the motorway (M8 an M77 I have seen them). Stuart thinks it is the X to indicate a lane closure, however I think it is something to do with gps and tracking people, possibly aliens. Someone should enlighten me.