How does one get a fire icon by their name to have it stay there?

Placing a bet of a small amount about half a mbtc then winning seemed to have given me one.

As long as you win a specific amount which is above the criteria to be listed on the high roller tab then you'll get the icon. I got it many times already although my bets were just small amount, but I hit high multiplier. So your bet amount is not the key, but your winning amount is the one that makes you get the icon.
Does it have any benefit other then showing in chat you have placed a bet and won a certain amount?
No direct benefits of getting the icon, but if you can get it many times then I believe you'll get surprise reward like what I and other players got some time ago. I received free $100 for being high roller not long time ago, so maybe they will give similar thing in the future who knows. I myself now prefer to use hidden feature so I wont get the icon, as most of the time I get the icon then there were many users asks to be friend and if I accept it, then most of them will only ask for some small amount of satoshi (beggars).