The issues is a state issue and has to do with passive electioneering. I had always been told that such is not allowed which is the law in PA however we had always limited to those working the polls and disseminating information. However, there is a law in PA that even voters are not allowed to wear t-shirts, buttons and the like. So Roger, you need to check Illinios laws.
NPR has a good discussion on the topic available here:
http://www.npr.org/templates/story/story.php?storyId=95333660