You just assumed your conclusion: that polite words are not part of the signal.

I think the word signal is being overloaded here. The signal here can be seperated into the core signal and the social signal. The social signal is also a signal and is necessary for the interaction to succeed but in the context of a signal-to-noise ratio it counts as noise because our goal is to extract the core signal; the social signal/noise should be there to the extent it is necessary to allow the core's extraction without unwanted side effects.

I don't consider anything in your comment to be the bad kind of noise and there's nothing I would cut, but the third paragraph contains far more words than it would have to if it could be pure core signal.