OT, but I've been seeing the "proud to be a co" thing on a lot of .co websites. I think I saw it on 500.co, last night. Seems like .co is trying to position itself as a premier, aspirational domain.
That's odd, why would the site owners care what .co is trying to do? I don't understand that banner at all...
It's possibly a banner ad in disguise, and the .co registry using this kind of promotion as a way to legitimize their ccTLD as a gTLD. Maybe the registry is providing some kind of sponsorship or kickback. I presume it's similar in nature to the sites that display the fact they're hosted by Rackspace that you see every now and again.
Looks like you're right, the .co registry is offering some perks if you buy a .co domain, so it might be linked to that: