We know that sounds affect energy at some level. The knowledge is common in a number of systems - mantras, kotodama, etc.
However, knowledge of hand mudras, specifically those ones used for cultivating/channeling energy through the chakras, as opposed to the vestigial remnants of energetic "postures", as harlan suggests, is not common knowledge.
My suspicion is that these seemingly "spontaneous" hand and finger positions do more than simply act as a focal point for channelling energy. The very specific finger positionings and even down to which hand over which hand, I'm sure, somehow "connects" the energy in different ways, and with different internal results.