I think the hidden cost is that if the signaler is called on the bluff, the signaler will be shown to not be fully committed to his or her pronouncements (and it will be reasonable to infer a good deal more flexibility in them than that).

Generally I think if someone has an intuition a case of apparently costless signaling would be valuable, his or her intuition is usually correct, but the intellect hasn't found the cost of the signal yet. The intellect's claim that only signaling that has costs is valuable remains accurate, as you say.

Which makes the signaling not just costly, but irrational.

It seems like its irrationality would be made contingent on some variables, so it would sometimes actually be rational costly signalling. Following through on a costly commitment clearly has costs, but why assume benefits to reputation aren't greater?

If you say "I will be careful not to betray lessdazed so long as his costly seeking revenge would be worth it for his reputation," you run into the paradox that such cases might not exist any more than one "[t]he smallest positive integer not definable in under eleven words" exists (Berry's Paradox). So long as my actions are best interpretable as being of negative utility, they get +3 stacking bonus to utility. Of course, I then run into the paradox because with the bonus I no longer qualify for the bonus!

A well made, RPG would state whether or not the bonus counts towards calculating whether or not one qualifies for it, but Azathoth is a blind idiot god, and for all its advanced graphics and immersive gameplay, RL is not a well made RPG.