Char to use as separator

[PATTON, BILLY \(SBCSI\)]

>From my questions today you may know that I'm doing some very convoluted
stuff.

I build targets with _  as separators

<flow>_<proj>_<bb>_<topic>_<target>

Problem is, any of these names may have a _ in their name
So separating on _ is a problem
So many of the chars are special to either shell or makefile

I've considered using __ that 2 under scores as a separator
Will this cause a problem within make or sh?