Happily graffiti wasn't a major problem for the Fair. It was there, though, and shows up from time to time in pictures. Let's take a look at one example.
Here's a closer detail of the building in the lower center of the photo. It was part of the Pan American Highway Gardens.
I imagine that this would have been removed in short order to help keep the Fair looking nice for the out of town visitors. Its just a good thing they didn't hold the Fair 10 years later!