In many services we use the image charts API
https://developers.google.com/chart/image/docs/gallery/dynamic_icons

This is deprecated since April 20th 2012 and can desapear at any time after April 20th 2015

For example it is used in the search map, the aggregation map and so on, in the GmapViewer.js file
url = "https://chart.googleapis.com/chart?chst=d_map_pin_letter&chld=" + (letter || '') + '|' + color;