Its perhaps worth pointing out that the tail rotor pitch angle depends (in nearly all helicopters) on two things, the position of the yaw pedals and the position of the collective. Many helicopters will fly at Vh with the pedals roughly in the middle, and also fly in autorotation with pedals roughly in the middle.
Therefore with normal flight collective position, full left (european) or full right (american) pedal may not give a negative pitch angle on the TR. It certainly will do in autorotation, partly because some negative pitch is needed to overcome the transmission drag (as TET says below), and also because a helicopter that does not require a large TR pedal input when going from powered to autorotational flight is a well designed one. In other words, in auto there is lots of negative pitch available, but its unlikely to ever be needed (esp if you do you EOL into wind!), and this is just a consequence of making the neutral-ish pedal position correspond to a slightly negative TR pitch with the collective down.
In some types, the amount of pedal travel to the left (EU) or right (USA) reduces as the lever is lowered - in other words if you have full pedal with the collective up, then lower the collective, the pedals are forced back towards the middle (best to try this shut down on the ground!). In some types this is not the case, perhaps to reduce the probability of a pedal jam restricting collective travel, with the inconsequential side effect that there is more negative TR pitch available with collective down than one could reasonably need.
HC