Since 2009 many Machin Definitives have been produced as self-adhesive Stamps with enhanced security features including semi-circular slits and an irridescent overprint.
During the course of 2010 stamps from most sources have been found with a new year code of MA10. In 2011 the code is M11L.
This is the 1st class from the Thunderbirds mixed content books of 6 with security print ROYAL MCIL.
SG Catalogue/Norvic cross-reference table - click here. See other blog entries for the history of the development of security Machins.