Signalling doesn't have to be that straightforward. A clever individual (of which we have a few) may choose to be significantly more circumspect, and imply that a piece of knowledge is obvious by omitting it from a statement that presupposes it, or alluding to it off-hand. We do this all the time, but I'm going to say that this probably has more to do with mind projection than anything else. It often simply won't occur to us to modulate a statement to encompass the receivers.

However, I don't know if this is a ploy we can entirely defeat just by making obviousness a bad word. If anything, that just requires people trying to make such a ploy to be circumspect...