Yes, that's right: McDonald's have trademarked a grammatical error.
In English, the nominative form of the singular first-person pronoun, "I", is capitalised, along with all its contractions (such as "I'm").
Not content with contributing to the increasing rates of obesity in children, must McDonald's make a contribution to ruining children's grammar too?
Perhaps McDonald's next posters will be "fully leet":
M(Ð0n4£Ð'$
1'm £0v1n9 17!
1'm £0v1n9 17!
Perhaps they will switch to the world's fastest growing language - LOLese:
mcdonuldz - i can haz cheezburga?!!1111oneoneeleven
Ceiling Cat will be most unimpressed to find His language used for such crass commercialism.