You can add overlays using:
map.drawOverlay({
lat: -12.043333,
lng: -77.028333,
content: '<div class="overlay">Lima</div>'
});
You must define latitude, longitude and the content of the map overlay.
Note: Also, you must define a height to the content.
Note: Also, you can define a verticalAlign, which can be top, middle or bottom, and horizontalAlign, which can be left, center or right.
Note: Also, you can define a click callback method, which will be triggered when the overlay's DOM element is clicked.