I found this out by accident. When measuring, the GM can see the measuring line, the players can see it, but the GM that is relogged in as a player can't see it. This leads me to believe that its supposed to work as the players shouldn't see it, but its a bug that they can see it. Although it would still be nice to have a way to either display the tool or not so you can show players something or just measure something hidden. Here is a screen capture. Notice the three yellow circled areas. I did this all on one computer with two different usernames, one is the GM obviously and the other a player.