You can read about vandalism of GM crops in this post by Karl Haro von Mogel on Biofortified.org.
GM and non-GM crops look the same. According to this article from the Los Angeles Times, “[t]o the naked eye, the white puffs of cotton growing on shrubs, the yellow flowers on canola plants and the towering tassels on cornstalks look just like those on any other plants.”
If you’re interested in learning more about the different types of methods used to develop new plants, check out the video below from University of Florida professor Kevin Folta:
If you have any additional questions, please ask.