i think in an american-style crossword if you abbreviate jackie C like that you'd expect the answer to be abbreviated in the same way... in a cryptic obviously either way woulda been fine
@MOehm underhand (without anyone noticing) = her cycling in und ("and" along the Rhine, i.e. in German) + and ("and" in the Lake District, i.e. in English)
@PDT ah, I see. Homophone indicators are usually words that refer to saying the word out loud somehow (like "reportedly", "we hear"), not sure if I've seen noisy (or a synonym) used as one. That's not to say it can't be used, of course.
