I'm looking for a noun which is kind of word or phrase that is used to indicate the existence of some unspoken knowledge that the speaker has.
For example:
Her use of the the word "pincushion" was a deliberate ___________ intended to let him know that she knew his secret identity, without alerting those she suspected to be listening in.
I've a feeling this word begins with an S and has 3 or 4 syllables, but am drawing a long blank in my memory…
Best Answer
Shibboleth comes close, though it's not used in the way you intend. Historically, it was used as a proxy test related to whether the person started the word with the sh- sound or the s- sound.