For anyone trying to
...in 2019, it's worth noting some of the code referenced here no longer exists (officially). Google discontinued support for the "MarkerWithLabel" project a long time ago. It was originally hosted on Google code here, now it's unofficially hosted on Github here.
But there is another project Google maintained until 2016, called "MapLabel"s. That approach is different (and arguably better). You create a separate map label object with the same origin as the marker instead of adding a mapLabel option to the marker itself. You can make a marker with label with multiple characters using js-marker-label.