Lol - I'm no use to you whatsoever as I only pick up the Mail once or twice a week when I can get it free from Waitrose, so I know there's no point in signing up to the rewards scheme myself.
I don't even have a Mail I can look at to enlighten you (it goes in the recycling bin pretty sharpish!) - all I know is there are some lottery numbers on the second page which are the same for everybody on that day, but there's also a unique 6-number code printed on the bottom of the back page. I always have a quick check when I get home that my unique numbers don't match the lottery numbers - that gives you an instant prize I think and possibly you have to claim on the day? But also I think you have an online rewards account that you submit your unique code to every day, and this gives you "points" - but what they go towards I have no idea! ;D
I always post on here when I have a unique code in case anybody who needs it wants to pm me - but nobody has asked me yet. I'm taking my cue from a thread on The Other Moneysaving Website which seems quite active - people share genuine codes there.
One of the issues is that you can legitimately buy your copy of the Mail and some naughty person has already eyeballed that code in the shop and used it themselves. Each code can only be entered online once. When I pick up my Mail in Waitrose I always pluck one from the back to be on the safe side.
Maybe joeg can throw a bit more light on this? I do apologise if I've got the wrong idea of how it works!