Spitfire EN951 'RF-D'

Is there any significance to this Spitfire? I have seen several paintings depicting this aircraft and the BoB Memorial Flight have AB910 painted as RF-D but is there a particular reason why?

http://www.airliners.net/photo/UK—Air/Supermarine-349-Spitfire/1210927/&sid=b2fdfac3ce40171754f851476b3a3ce2