At the moment I'm working with a paper from Kimball A. Milton (a student of Julian Schwinger) and he uses a notation which I can't find anywhere. He wrote (page 33 eq. (4.19) http://arxiv.org/abs/1503.08091):
$$p_a(t) \cdot [q_a(t+dt)-q_a(t)]$$
He says this $\cdot$ denotes the symmetric multiplication of the $p$ and $q$ operators. But what does this mean? I can't find a definition of this dot product.