The + sign?

Well I’m sorry to start a whole new topic about this and I’ve tried to search for the answer myself…… but, what are the little + signs for at the bottom of a comment? 
Is it to show you agree with a comment or like a comment? 
Thank you. 

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  • Also, I think some people will upvote a comment to demonstrate that they have read it.

  • I think people treat them as like or agree too though. I actually dislike having partial comments at the top, especially as they are only the start of a comment, and out of order and context, so I just scroll past them. I'd switch that feature off if i could! Although I do sometimes press the up arrow if I like a comment, but I'd rather it was just a normal like or agree type thing!