Anniversity? US Capitol Grounds Memorial Tree

Strolling through the Capitol grounds we noticed a sign on one of the trees. Many of the trees are dedicated to different people for a variety of reasons, while other name plates simply identify the type of tree or plant that is growing in the spot. There was nothing really unique about the sign itself but something caught my eye. Upon closer inspection, we noticed a weird word ... Anniversity? We both looked it up immediately on line and could not find it on a website or in the dictionary. I even sent a picture of the sign it to a friend who knows everything about words and the Capitol, and she never heard of it. So, was it created this way on purpose, or is it a mistake and someone was hoping it would not be noticed. If you have ever heard of this word, please help us out! In the mean time, shame on the person who approved and made it!