Head down and ears to the side, instead of pricked forwards in attention with their head right up, generally indicates that they are not feeling threatened and are not threatening you either; it's a netural posture where no one outranks the other.
Aggressive signals are easy to spot - ears flat back, teeth bared, head up - sometimes being tossed around. Not all of them are necessary at the same time.....but they are BIG clues that that's a good time to leave! And whatever you do DON'T run