So I ended up going there yesterday and I can confirm that it's NOT posted. It's actually inside the big shopping mall there (Hawthorn Center) which I did not know. I thought it was a separate building somewhere in the general area. I can confirm that the mall is NOT posted either, which is nice. Knowing Vernon Hills, I figured it would be posted by default, but it's not, so I think I might visit there more often.
There is big AMC theater in the mall as well and as far as I could tell, it wasn't posted either from what I could see. Once you're in the mall, you can walk right up to the theater ticket area and buy a ticket, then you must go upstairs to get to the movie theatres. I didn't see the upstairs area, so I don't know if it's posted up there or not, but you can't get up there without first going through the ticket lines and buying a ticket, so I'm guessing it might not be.
If it's really not posted, I might go see some movies there. I haven't been to a movie theater ever since getting my CCL, so it would be nice to find a movie theater that doesn't ban CC.
I heard that the mall was posted at one point, but apparently they removed the signs. I think it's a smart move for the mall to allow CC since they definitely need all the customers they can get.