I heard tonight from Mike Reischl of the Way Out In Left Field Society. They are working with UIC to get a new marker at the site of West Side Grounds and the removal is only temporary.
For now, I'm closing comments on this post. When there's a new marker, I'll update this and reopen comments. Also, for now I've temporarily removed (not deleted, just removed) the original post from the front page, and I hope to have more information from Mike soon.