17 is a year code for when they were printed, and B means the stamp came from a Business sheet of 100.
Aha. You are not a philatelist. Yes, there are 'secret' anti-forgery symbols on stamps. The year of production ('16', '17', '18') appears in places amongst the 'ROYAL MAIL' wording. Common location is on front of The Queen's nose. This is well known.
“Hidden Source Code And Year Codes” http://deltastamps.com/pdf/Hidden%20Codes.pdf
Royal mails usual counterfeit prevention method is just to put the prices up every 6 months so no one has a chance to make their own...
Completely wrong. They normally do a price rise once per year in April. And this does nothing combat fogeries. As most stamps are NVIs (Non-Value-Indicators). This means that they show "1st" or "2nd" and are valid whatever the current price of purchase of 1st and 2nd class stamps.
I don't think it was a serious suggestion..
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