On some of the older F-16's used by the Thunderbirds (I am not sure if they still have the Block on it), have a multi coloured block on the side of the plane just behind the cockpit, I was wondering if anyone can tell me what it is?

It is a "flag panel", with the flag of every country they have visited, as well as the "MIA/POW" flag. It is still on the jets today.

Thanks for replying to that, I noticed that just after I posted btw, love your pit Gunner.