Still a little fuzzy
Start with FAR 23.777. Also, 23.1141-, and 23.1555
Thanks. Yep, those seem to be applicable regs. But they still don't seem to unambiguously answer the question.
23.777(c)(3) and 23.777(d) specify how the engine controls should be placed. Check.
23.1555(a) specifies generally that the controls must be marked, but does not specify how they must be marked.
And that's the core of my question. Does "mark" necessarily mean "text placard"? Or can "mark" be satisfied by other means? In the case of the throttle, prop, and mixture knobs, one might argue that their function is already marked by putting them in the standardized locations and making the knobs have the colors and shapes that universally identifies that specific control per the FARs:
The required motion and effect of each control is specified in FAR 23.779(b)(1)
The required unique shape of each control is specified in FAR 23.781(b)
I couldn't find a FAR that specifies the standard color of each control (black - blue - red). Maybe that's just de-facto standard?
In any case, all of the above would seem to adequately "mark" the control for its function. So I'm wondering if text is still also required by the FAA's interpretation of the applicable FARs?