I'm not surprised the stat cards don't work right now. ND just made a big change to their stats website, so the format of the information is different (which is where the stat card site is getting its data). The bigger issue is that the new stats page requires you to sign in to get your data. Previously, you could query the site for any user without having to log in, which is why a 3rd party site could get your stat data to make those cards.
Maybe they will change the stats page to be more accesible.
Ahh that makes sense. So I guess it should be working in time. But other players cards work. Yours does, for instance. Oh well, it's not that important anyway. I'll just wait lol
EDIT: Now that I look closer at yours its not even close to accurate lol. It says you have 608 kills and over 15k of them are melee? Thats magical... 
Mine is probably stale. I think they only regenerate once a day. If my 24hr window hasn't gone by yet, then it hasn't had a chance to hit the new stats site and fail.
Oh, and technically, the stats are "correct". You have to know the context though.
The melee and stealth kills listed on the stats website are for both competitive and co-op.
The games/wins/losses pertain only to competitive and co-op hunter.
I have only played co-op since 11/1.
You put it in your signature in My Settings.
Just paste the HTML code that will look something like:
<a href="http://naughtykennel.com/u3sc/"><img title="Uncharted 3 Stats Card by the Naughty-Kennel.com - Click here to get your own!" alt="Uncharted 3 Stats Card by the Naughty-Kennel.com - wx327" src="http://naughtykennel.com/u3sc/art3/wx327.png"></a>
