What is this decorative motif called?
I don't know if this was intended but after looking for banded column style I ran into rustification or rustication:


  Rustication is a form of exterior ornamentation particular to buildings in the classical style. It is defined by projecting stones with sunken joints or grooves conveying an air of deliberate roughness and strength.


That is not compelling but the article goes on to describe different kinds of rustication. It is a broad definition but a specific style of rustication is:


  Picked-work or a simple chiselling or chipping of the stone surface to produce a general rough effect 


Two of the examples on the page do my connection more justice. Click to enlarge in both cases.

 

It seems obvious from the photo in the question that this is not carved but it looks to be emulating picked work rustification. I can almost draw a line of symmetry down the middle of your picture but that might just be looking for a pattern that does not exist.  

Searching for images of rustication yields similar results.