See How The Cubs World Series Rings Were Made
For the fans, a championship is symbolized by the trophy. The Lombardi Trophy in football, the Stanley Cup in hockey, the O'Brien Trophy in basketball, and the Commissioner's Trophy in baseball.
For the players, their part in a championship is symbolized by the ring. A symbol they will wear with pride for the rest of their lives. (Unless of course they run into financial problems and have to hock it.)
Last night, at Wrigley Field, members of the 2016 World Champion Chicago Cubs (still sounds weird) were given their championship rings.
This video details how they were made. Cool stuff...