They seem to be called "wall plant-ons". Christies had at least one for sale a few years back, which you can look at here.
According to the auction blurb, they're bits of wood that have been painted and lettered. I'd imagine in the props department.
As an homage to the TOS prop work, they actually made the internal works for the "wall plant-ons" in the form of "busy boxes" for Star Trek: Enterprise.
More informative, from the same auction listing:
No one is quite sure what these gizmos were supposed to be on the original Starship Enterprise. Series art director Walter M. Jefferies simply wanted some technical-looking hardware to add visual interest to his corridor sets. The show's perpetually-constrained budget did not allow him the luxury of creating such things from scratch, so he looked around the studio for something that he could use. Stored in a soundstage basement, Jefferies found a collection of intricately-made hardwood shapes. They were old tooling patterns to make the inner mechanisms of obsolete camera cranes and dollies. Since the patterns hadn't been used for decades, Jefferies thought they might do well on his starship. Decades later, the Paramount special effects shop spent thousands of dollars re-creating Jefferies' inexpensive find for "In A Mirror, Darkly" in Star Trek: Enterprise. These unusual wall decorations remain a signature of Matt Jefferies' ingenious vision of the 23rd century, even if no one knows what they did.