With my runners, before they became full-fledged adolescents and rather standoffish, of the eleven, there were three or four who seemed to like their sides being stroked. Two seemed to enjoy any pets - sides, back of the neck, top of the nead, top of the tail. The rest just walked away when I touched them.
Tail wagging seems to be a happy signal with mine. Haven't seen head-bobbing yet - they are only seven weeks old.
With the runners, they also have a stand-up-straight, quack loudly greeting that roughly seems to translate to, "what goodies did you bring us?"