To combat forgeries and the illicit re-use of used but uncancelled stamps the Royal Mail in 2009 introduced a number of security features on self-adhesive stamps, primarily the 1st and 2nd class Non-Value Indicators (NVI or Forever). A number of valued stamps also have been issued with the security features.
To make it more difficult to forge stamps most new definite stamp issues are overprinted with an iridescent ink of the words “ROYALMAIL” (The stamp images have been enhanced to show the overprint). The overprint will not show clearly when photocopied. If the special iridescent ink is not used in the forgery it becomes very obvious to anyone the looks at these stamps. In 2012 a new type was issued with the words “DIAMOND JUBILEE” replacing the “ROYALMAIL” overprint.
To prevent the undamaged removal of stamps from processed mail, four U-shaped die cuts forming two ovals are made one on each of the bottom corner area of the stamp. The slits are designed to disintegrate the stamp when trying to soak it of the envelope paper.
To assist in product and quality control, in 2010 the use of codes in the overprint was introduced to allow tracing the source of the stamp issues when usage problems are encountered. These codes in one of the words identify the issue year and source of the stamps. The following Table identifies the source codes. The source code appears to the right of the Queen’s head, usually but not always, in the upper right area. To the left of the Queen’s head the year code changes the last two letters in one “MAIL” word to 10 for 2010, 11 for 2011 etc.
For the stamp collector these security features makes it relatively easy to identify the catalog number of these stamps.