Thinking about this further, it seems to me that a setting that allows people to positively select to be “I don’t want to NOT see them” would be the way to go.
If you consciously turn that on, then getting an intrusive symbol seems OK.
Doing it by default does not seem OK.
Agreed … to actively ignore, right?
Agreed, no modal panel where somebody has to click “OK” or “cancel” before game goes on, that would be annoying.
So … blinking red question mark 
I personally would not be comfortable with that, if you mean “as my cursor” or “on the board”, without me opting in to it.
An undo request is something on the side. I should be able to ignore it comfortably, not be continuously reminded about it.
If you opt-in to being continuously reminded, then any sort of in-your-face reminder would be suitable.
I agree with Eugene here. How we have it now is fine for default, and I would be ok with providing an opt-in option to make it harder to not notice an undo request (such as a blinking red question mark).
I meant 
on the last played stone, the one the opp. requests to undo.
I‘d think opt-out of undoing means the opponent also gets a notification that the opponent has disabled undoing—and thus you‘d never get to see it.
This should also be an explicit option in a game challenge invitation, and shown to to the invited person.
Anyway, however it is done, whether undo request is allowed or not in a game should, IMO, belong to the game settings/invitation, and be transparent for both players before the game.
No idea how to handle this in tournaments … maybe in 30 or 40 years categorize in undo/no-undo tourneys or something 
Note: I can’t remember when last time I asked for an undo, as I personally would rather live with the mistake—misclick or not—and learn from it, but usually I have no problem granting an undo.
A dialog box opens before move is confirmed:
An undo was requested. Are you sure you want to submit
your move and ignore the request? (Cancel/Submit buttons)LOL no, not even for me 
Works for me. But only as long as it is opt-in to get this dialog.
You don’t want to give trolls a tool to timeout you. In blitz/live games everything demanding your interaction is a tool to force someone to timeout.
There is also no move confirmation for one click submit.
To be honest, i actually like the idea of having a question mark instead that circle on last move.
Now the “problem” (well i havent really considered it being a problem per se) is that when playing corrs, i tend to glance at multiple board thumbnails on overview page, without seeing an undo request from my opponent. And sometimes after choosing where to play, i open the game only to see that my opponent didn’t meant to hane and i’ve been reading the cut for 2 days for nothing.
Another mild annoyance is that on mobile, the big blue button for ‘submit move’ / ‘accept undo request’ is just barely low enough the get hidden when there’s a minimised pm window. So on mobile, you better close all your pm’s before playing, or you won’t see undo requests by your opponent before scrolling down to submit your own move. (unless you play on mobile without using ‘submit move’ thing, in which case you’re prolly mentally ill and you don’t even care about undos, since half of your own moves are misclicks anyway…)
In both cases - playing corrs on mobile or by the overview page on computer - it would be nice to see undo requests from my opponents before i am ready to play my own move. Simple question mark on the last stone would help a lot with this in pleasantly unintrusive way.
You don’t want to give trolls a tool to timeout you. In blitz/live games everything demanding your interaction is a tool to force someone to timeout.
Could there be a way for OGS to add a courtesy time for both players to consider the undo? In Blitz or otherwise?
There is also no move confirmation for one click submit.
Could there be an exception for an undo request situation?
None of this is going to happen. I could give you many reasons why none of it will work in practice, but the short answer is simply no.
Asking for an undo shouldn’t happen often. In the rare cases it does, typing in chat explaining why you asked for one (“misclick”) seems like a reasonable solution. If chat is missed by the player, undoing sequences is possible but I’d prefer the misclicking party dealing with it and playing on.
If “undo” is going to become more alerting, I’d like an option to turn it off entirely (which I would, for ranked) like Eugene suggested.
One of the reasons this won’t happen (sophisticated undo-alert systems) is because (as snakesss says) this is a rare thing anyhow, so any effort spent in implementing changes in this area would need to be minimal to make it into “the list”.
Changes that are purely visual have a better chance, because more people can work on that.
If you can say “in this case, where you display XXX could you instead display XXX”, that’s a visual change. Even “adding a setting to control how its displayed” is conceivable.
Changes that required “the way it actually works” in the area of “undo” seem extremely unlikely.
Could you provide some criteria or possible avenues for improvements that are tractable? It would be a shame for a reasonable site improvement request to be classified as impossible.
^^ I thought I just did that 
Suggestions that are purely visual, which can be described as a change in the way we display something, are tractable.
(I appreciate it can be hard to guess whether your suggestion is purely display or not… but at least you can be sure that if it is not you will get told )
Now and then I’ll skip someones undo request essentially from playing quickly and clicking submit before realizing there was an undo requst.
I think this would basically solve it no matter what. There has to be a small population of players that never play with sound, so a beep wouldn’t really help them. This would just be answered yes or no and done regardless of the situation, right?
You can’t do that live, because it consumes time.
Unless I suppose it pauses the game. Which would be a back-end change.
Also in a blitz game it could be abused to milk extra reading time
I mean may I ask what is the point of playing blitz if you’re going to request an undo?