That's terrible but I find it funny because it doesn't make sense unless Rush wrote it and that's what I'm thinking. I'm just adding it into my headcanon that Rush has some issues with the French speaking people.
I do remember that this picture was a big discussion on several SGU boards, and some people get really angry about it. Though, I don't think that this is the best joke I've ever seen, it's also not really a drama. I don't know for sure, but I guess it has something to do with the animosity between the English and French speaking people in Canada. Since it's handwriting I'd think the resposible people for the show, might know in between who this did, and I bet the offender got some long ears for doing it.
Hmm, not sure whether it's really a JOKE, but it got for sure accidentally recorded, so, it was of course a mistake. Only a very few people recognised it, but those who did, told everybody about it, and some were indeed angry, and some of those some, found a new argument why SGU is so bad... So, honestly, you didn't missed anything.