In the movie, Inception, a totem helps a totem owner eliminate the possibility that you are in someone else's dream. The explanation being - only you know your totem's unique uncommon feature, so if that feature is present, then you are surely not in someone else's dream because the dreamer wouldn't know about the secret feature of your totem.
However, how does projection not affect this scenario? If Cobb is able to project Mal inadvertently into another person's dream, why wouldn't he not inadvertently project his totem's secret feature also into another person's dream - thereby invalidating the premise of a totem?