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I think some sort of notation rather than bolding would be a bit more appropriate. What if users prefer to bold the poll options, that would completely defeat the purpose of that. I like the arrow but I do suggest moving it to the left.
The check mark couldn't work as there's no way to know whether it will display properly. An image is the only other option, and that could work, though I don't feel that it needs to be that in your face.