In the past we have seen questions on Puzzling Meta about what to do when an OP hasn't accepted an answer and similar. However, these questions tend (just by their nature) to end up being answered with the shrug-of-the-shoulders response, "Not much we can do, I'm afraid..."
After all, as @GarethMcCaughan says in his answer to the linked post, when an OP hasn't yet accepted an answer "no one can compel them to accept anything" - it's just not in anybody's power to insist that a checkmark is given after a certain amount of time has passed - only the OP can push that magic button. Plus there may be a very good reason that the OP has not granted the checkmark - the answer may not yet be complete to the level of detail they had hoped, for example.
There are, however, a substantial number of questions out there where what is clearly a correct answer has been given (often even acknowledged by the OP in a comment on the answer) but where the green checkmark has not been awarded. As a user of the site I confess that I find it a tad frustrating (to the level of TUT/HEAD-SHAKE/EYE-ROLL, nothing substantially higher!) when I come across a puzzle that I think has yet to be solved, only to find that it definitely has been, just the answer has not been marked as correct. Also, I can appreciate (like in the case of @KevinL in the linked post) that it can feel offputting not to have your correct answer acknowledged, especially when you put a lot of work into providing a solution.
Now, obviously, we can do nothing about all the questions which have been set by users who have since left the site, closed their account, or have not logged in for a long time for whatever reason. But on this site there are still a large number of un-checkmarked questions that have been asked by regular Puzzling.SE users. (Naming no names, and linking no examples, because this is not intended to 'shame' anybody...)
I propose that we hold a Checkmark Amnesty, either as a one-off event or as a regular occurrence (say, on the first of each month) where regular users of the site commit to spending just a few minutes to (i) look over the questions they have previously asked and which do not yet have a checkmark awarded, and (ii) award checkmarks where they should have been given (or (iii) possibly even consider adding hints or offering bounties on questions that remain unsolved).
This would help - in a small way - towards 'doing the housework' at Puzzling, cleaning up a little from time to time. Ultimately, this would make it easier for users to find puzzles (or puzzle-related questions) that actually do still require a solution, and set a good example to new members of the community.
My reason for posting this here is not to ask "SO WHO'S WITH ME?!" (although I do hope that those who read this post might consider adopting an attitude like this themselves, if they don't already) but to ask whether those who run this community - the mods, primarily - would consider incorporating this somehow into the overarching ethos of the site. The fact that the checkmark functionality exists at all is indication that the community believes it is important to mark correct answers as such, but the occasional comments left by conscientious users saying "Does this need a green checkmark now?" are often ignored, and while nobody wants a 'green checkmark police' hunting down others who they deem to have fallen short of a certain standard, or any notion of 'shaming' other users into closing things off properly, perhaps a regular reminder in the form of a banner message or a meta post might help keep things in shape and catch those questions that just slipped through the green net. Maybe even just a greater emphasis in the site tour or other materials aimed at newcomers...
I do not delude myself into thinking this is 'the answer' to the problem. Even an amnesty will not fix all of our un-checkmarked questions, of course... but it might go some way to encouraging others to take up this behaviour regularly and instil some 'best practices' into the ways we all use this site... And who knows, maybe it will inspire somebody else to come up with a better solution!
Thanks for reading.
NB I repeat, this is not an attempt to 'shame' any users into taking action, just a way to nudge a conversation into happening... This question most likely arises out of my own deep-rooted preference for closure in life!