The vipers I have have a sticker on them but no markings.
In may 2009 the requirement for markings on exhausts for MOT's was removed. The MOT guy can fail it for the excessive noise, leaks, damage and or bad fitting. Not for no markings.
However MAG states that all exhausts must have markings.....
Others state that small exhaust manufacturers can bypass this requirement due to their low volume output.
So, you don't want to mark something up yourself (Setting your self up for a possible perverting the course of justice) Sticky labels, hummm, PC Plod with thinks you have made them up yourself (My Vipers come with sticky labels

ebay guy is selling metal straps with the right marking on them, but again a possible perverting the course of justice.
Viper baffles are "e" marked but will be inside the exhaust...
Think I will leave the cans as they are and see if I get stopped. The question is does anyone here have the definitive answer?
Stephen