On the Canon stand, which is now not going to be there, there were normally lenses attached to bodies for you to try....if you could fight your way to the front. I honestly can't remember what it was like at the Nikon stand

Sigma tend to have a few on display, but general not as many as the other two. On the Canon stand they use to let you put your card in and take a few shots so you had a record of what the images were like...again with Nikon I dont know....I am actually starting to wonder if I have ever been onto the Nikon stand :|