Somebody1 decided that the area known as the Northwest Angle in northern Minnesota has turned into a potential security hole for terrorists arriving from Canada.
The northern-most arrow indicates traffic funneling through Minnesota's last one-room schoolhouse.
Watch the web cam at Flag Island for suspicious behavior. If you see anyone leaving by boat without a fishing pole please contact authorities immediately.
1Overheard on an Air America Radio news report, but have found no verification from online news sources. (Update: Link)