Verb for subtracting the mean? Is there a verb for removing the mean or DC component of a signal? I am trying to name a flag for doing just that.

"Normalize" can mean many things, so I don't think that would be a good choice.
I've heard this referred to as demeaning a signal, or applying a DC notch (or, in some more hardware-related domains, a DC block). More generally, it might be called just highpass filtering the signal to remove the DC component.