While adding some images to the stamp wiki I noticed the perforations for the 2008 Rescue at Sea set had some odd perforations! It turns out the perforations form the dots and dashes for SOS in Morse code.

I learn something new everyday!
Rest of the set can be seen at
http://www.stampsoftheworld.co.uk/w...escue_at_SeaSOS is dot dot dot dash dash dash dot dot dot
Drew