Symbolism, Imagery, Allegory
Fun fact: in Shakespeare's day, "nothing" was pronounced as "noting." This clues us in to the fact that noting is central to all of the action: there's much ado about noting. And we mean all sorts of noting.
Noting is a motif throughout the entire play. Early on, it shows up in the form of special observation:
CLAUDIO Benedick, didst thou note the daughter of Signior Leonato?
BENEDICK I noted her not, but I looked on her. (1.1.158-160)
But the notes don't stop there. They also pop up through music (as Benedick jokes about sheep’s guts as strings on an instrument, when Balthasar plays his notes, etc.), and also through written notes (like the letters that ultimately reveal Benedick and Beatrice’s love at the end of the play).
Ultimately, the play revolves around misnoting—the problem of people wrongly interpreting what another person does or says. Benedick and Beatrice are manipulated into noting false conversations about their mutual love, and Don John sets up Claudio and Don Pedro to wrongly observe (or misnote) Hero’s loyalty.
The play constantly points out the difficulty of observing correctly, as observation is always subject to interpretation, and interpretation is often wrong. This doesn’t mean that misnoting can’t have good outcomes—after all, Beatrice and Benedick do get together as a result of it—but Shakespeare is essentially laughing at the ridiculousness that result from misnoting.