WW "etiquette" question

[pudley4]

Last turbo game I was a villager and saw two of the players reading and sending PMs before the game started. It was pretty obvious they were wolves so I PMd the moderator to let him know. Since it was 2 (out of 3) wolves, it would have been a huge advantage and I asked to be replaced.

What's the consensus on seeing players who aren't invisible on 2+2? Is it any different from having one of the players on your AIM, and seeing them go from offline to online, or from away to active? Is it best to tell everyone in the signup thread to set themselves to invisible? Should it just be declared illegal?