Occasionally people will thank for an answer in the comments and write that the suggestion worked for them. Is it acceptable to ask them to accept the answer or upvote it instead, as seems preferable according to this help section entry , or is it considered bad form?
If it's clear that the asker is satisfied with the answer, and it looks like they are new to Stack Exchange and don't know about this feature, then it's a good idea to explain in a comment that they should mark the answer as accepted. Basically, if the asker has left a comment under an answer saying something like “thanks, it worked”, then reply to this comment and explain about accepting answers. You may leave a comment such as this one:
@bob Welcome to Stack Exchange. If this answer solved your problem, please indicate that by [marking it as accepted](http://unix.stackexchange.com/help/someone-answers) by clicking the check mark next to it.
Just to be clear, you should do this only if the asker has explicitly indicated that the answer solved his problem, and it looks like they didn't know about accepting answers. Don't do this if you merely believe that your answer is correct: the asker may not have had time to test it yet, or there may be a flaw that you didn't see, or he may just be waiting a few days to see if better answers come in (which is perfectly ok).
You can do this in a comment and delete the comment after the accept-vote has been done.
Accepting answers leads to good answers. IMHO it can not hurt to say so.