I thought that a high level mage, or a psyonics PrC (if it's possible) could send messages to people using there mind. You would probably have to make it like an ear of telepathy or some thing like that, but it would be a good way of sending in game tells.
I was also thinking that you would have to do a spot check to notice if the person that is sending the message is looking at the other person funny due to all of the concentration needed to use telepathy.