Presently the only ways to point out an error in a post are adding a comment and editing the post. However comments are not very visible in particular if a post has already many of them. Editing the post does not have this drawback, but it still may not be what one really wants, in particular if one does not know how to correct the error.
Therefore I propose to make it possible to set an "error flag" if one finds an error in a post. --
Such an error flag may show up as a warning sign on the left margin below the voting arrows.
A description of the error could be displayed when clicking on or moving the mouse above that sign.
I suggest to make an error flag bump the post like an edit, and also generate notifications to the same people as an edit (plus the OP of the question, if an answer is flagged).
I suggest that error flags could be removed when editing the flagged post.
It should be possible to search posts with error flags.
This feature request is motivated by the thread Dealing with possible incorrectness. I originally posted it as a proposal here, and turned it into a formal feature request following a suggestion by Francois G. Dorais.
Update: Proposal withdrawn due to rejection by community -- see poll below.