You can render your icon using the SVG Path notation.
See Google documentation for more information.
Here is a basic example:
var icon = {
path: "M-20,0a20,20 0 1,0 40,0a20,20 0 1,0 -40,0",
fillColor: '#FF0000',
fillOpacity: .6,
anchor: new google.maps.Point(0,0),
strokeWeight: 0,
scale: 1
}
var marker = new google.maps.Marker({
position: event.latLng,
map: map,
draggable: false,
icon: icon
});
Here is a working example on how to display and scale a marker SVG icon:
Edit:
Another example here with a complex icon:
Edit 2:
And here is how you can have a SVG file as an icon: