Greetings!

Got it. The photoshop equivalent was expand. I had tried to use layer effects, but that kept giving me anti-aliased / blurred edges.

I selected all of the text (I like to keep it as text to allow later modification as new hard drive sizes and add-ons are installed), expanded the selection, and used the exact background color from the stylesheet. This way, people using the default (empeg) style sheet see a plain white sig without a border, everyone else will see a 3 pixel outline that matches the "darktable" element - #333355.