so there are a few examples of this on the site already. see 'in progress' 'inactive' etc. this is close but not quite what I'm talking about. there is already a tag preference system and what I am suggesting is in a way an extension of this.
I personally avoid m/m combinations but I frequently see stories that list the code 'for completeness' with a disclaimer in the blurb. because of this I do not want to 100% block the code, however I would love a quick visual que that the code is there.
so why did I call it a traffic light? well think of it as green for a favoured code, amber for a caution code and red for avoid but not exclude.
the logic wouldn't be onorous but would definitely require some thought and may be somewhat CPU cycle expensive compared to a default parsing but it could be a useful cue / key for those wanting a little something extra in their feed.
it's a couple of decades since I tried my hand at programming for the web. I don't think perl was even fully standardised, css didn't exist and iFrames were still all the rage. html 1.0 and 2.0 and lynx and then Netscape days. yes I'm 'that old'. the web wasn't even publicly available at that time, you had to have an academic account to get online and gopher, pine and archie still held significant sway.