As you may have noticed, both in "EAT MOR CHIKIN" and the ad in the picture saying "GIT FREE CHIKIN", the cows are using mispelled English words. This is to make the ads more memorable, and it works, because let's be honest, cows don't speak perfect English! This particular advertisement was for Cow Appreciation Day, where if you wore a cow costume (like the cow in the picture) or cow-related clothing, you would get free chicken.
And before anyone emails me to ask - no, I didn't do it. I had to work that day, unfortunately!
Learn more about the cows: Chick-fil-A website