Where does water in shower plumbing go after a shower?
As far as I know there aren't any return valves in these shower systems.  

You will have a column of standing water remaining in the pipe.
(When the shower isn't used for a couple of weeks you should always run the water a few minutes before using the shower to get that stale water flushed out. It is an ideal place for bacteria to develop. In hot weather just a week is long enough for Legionella to develop.)

If the pipes and fittings are dry the drip is coming from somewhere else. Noise traveling along pipes can do strange things and it is quite possible the noise comes from somewhere else. It may not even be a drip you are hearing but something similar that you interpret as a dripping noise. (Hot water pipe or the boiler cooling down and making a ticking noise comes to mind. This can sound like a drip.) 

What I have encountered myself:
After the shower is shut off that pipe filled with water going up to the shower-head cools off. Cooling causes it to shrink slightly (how much and how fast depends on the pipes material and the ambient temperature) forcing a little bit of water out of the pipe into the shower head.
That water then drips from the shower-head to the floor. Dropping with a noticeable sound on the basin below. (Often people don't notice this drip as the basin is wet anyway after the shower.)
Or, if there remains some standing water in the shower-head itself, it drips into that little pool inside the shower-head. Sound-transfer/amplification will do the rest.
This sort of dripping typically starts 3-5 minutes after the water is shut off and stops after some time (typically another 3 to 5 minutes) when an equilibrium is reached in the pipe.