Is it acceptable to ask for upvote/accept in an answer when submitting it?

In my experience, new users tend to have a hard time to discover the checkmark by themselves. Not sure what the problem might be, whether that's too much of a Western symbol or whether it doesn't contrast enough with the rest of the page. I suspect the latter.

So following up with a comment like "Please close your question by clicking the checkmark to the left of the answer that helped you most" is a public service message in my book. Strictly a comment.

In practice I try not to nudge the OP unless I get a "thanks" comment from a new user and even then I try to keep my response informative...

The exchange usually goes a bit like this:

Received comment:

Thanks works great! Thanks so much!

Check to see if user has ever asked questions/accepted answers before. If they have leave it be. If it's their first question or they haven't accepted any answers yet:

Glad to help, if this answer solved your problem please mark it as accepted by clicking the check mark next to the answer. see: How does accepting an answer work? for more information

I think it's reasonable to inform new users of how to acknowledge answers by upvoting those that are helpful and accepting the one that was used or best resolved the issue. Many new users simply don't know that that's how things work. Sometimes they'll post comments like "Thank you so very much!! That worked great, you're a lifesaver" without accepting the answer, because they don't know better. That's not only frustrating for the answerer, it leaves many questions with an unanswered status after they've been resolved, which isn't good for the site.

It doesn't always work very well to wait until they've posted a "thank you" comment to educate them on how to acknowledge answers, because many (probably most) first-time posters don't become regular visitors. They'll post the comment, then not come back to the site for a long time, since they have no reason to come after their problem has been solved. If you wait for the "thank you" comment before informing them, they might never see your explanation. Or they might try a proposed answer, see that it works, and not even come back to leave a comment. This isn't necessarily out of rudeness. It's often more a case of "out of sight, out of mind" for people leading busy lives.

I've often informed new users of how to accept or upvote answers, but I propose following these guidelines when doing so:

• Always use comments. It's no more appropriate for inclusion in an answer than any other explanations of how to use the site.
• Rather than trying to reinvent the wheel, you can keep the comment brief and provide a link to the help section that explains what to do when your question is answered (https://meta.stackoverflow.com/help/someone-answers). This has the added benefit that once they've been directed to the help pages, they might read other sections.
• Check their profile to see whether they have never accepted an answer before. If they've accepted answers in the past, then they obviously know the drill, and "informing" them of what they already know is unnecessary and smacks of lobbying.
• Never lobby for your own answer. That's pushy and gauche, especially if there are other answers. Even if there are no other answers, the asker shouldn't be prodded to accept an answer if they haven't indicated that the answer provided a solution. Explain to the user how to accept an answer, and be careful to avoid even the appearance of advocating for your own answer.
• Make it clear that you're not specifically asking them to accept your answer and that you're not pushing them to accept an answer unless the issue was resolved by posting the comment under the original question rather than under your answer, and using comments like "if your issue has been resolved, please mark the answer that best resolved it as accepted".
• If the user has specifically indicated that a particular answer resolved the issue, then it's okay to post the comment under that answer and imply that they should accept the answer. It's still in better form to start with the word "if" rather than just telling them they should accept the answer.
• If you post these kinds of comments when you've answered a question, consider doing this for answers other than your own if you see a user who has never accepted or upvoted an answer before acknowledge a solution by means of a comment. Remember, it's not about you, it's about teaching newcomers how things work at this site.

Coincidentally, just last night I was thinking about suggesting a feature that pops up a message explaining the proper way to acknowledge answers any time a user who has never accepted or upvoted an answer posts a comment containing the words "thank you" or "thanks" in response to an answer to their own question. That would eliminate the need for the last two bullet points.

The answer should be able to help other users solve a similar issue, as well as the OP. Including something which alludes to requesting upvotes or check marks does not add anything useful to the answer and should be avoided.

If the user is very new and has no accepted answers then just be patient. Usually they will eventually figure it out and come back. If they post a comment on your answer indicating it was the correct answer, then it is appropriate to reply with a reminder that they can accept your answer by clicking the checkmark if it was the correct answer.

Moreover, new users sometimes are not used to the speed at which questions are answered here. Personally I think it is awesome that questions get answered with the speed they do. Back on point, sometimes the user has posted the question and left with the intent of returning later to review it.

All in all, there are a lot of reasons for users not immediately tending to your correct answer and I think the best advice would be to be patient. If you are answering questions with high quality answers then the upvotes and checkmarks will come.