I jokingly thought about adding something like that already.
Basically:
(^Paywall(ed)?)$
->I'm going to contribute nothing to the discussion except whine that you didn't cater to my laziness and make my laziness everyone else's problem until someone else replies with an archive link I could have easily gotten myself
This is very close to what I had in mind when saying "remind yourself not to interact with certain topics". That any time a comment contains a certain keyword/phrase, it could replace the entire comment with "I am a person not worth talking to".
What I have in mind would be a simple pair of textboxes for each filter policy: one for the regex pattern to search for, and one for the string to replace it with. Then a checkbox or something to toggle whether just the matched string gets replaced or the entire comment gets replaced when the pattern matches anywhere in the comment. Then, the user can add as many policies as they like.
As for indicator, I think what I would prefer as a user is a little icon next to the edited indicator, and then the ability to view comment source (which is already a feature on many clients). Though that is not really addressing the problem very well, as people viewing the screenshot need to understand what the icon means.