I have just updated this plugin marginally so you can add an URL to specify the map marker, and you can use a single character for a label as per the googleMaps API. If you do not specify an URL to an image file, or the URL is invalid then the standard marker will be used. The images obviously have to be stored on a webserver of some kind, but you can modify what image is loaded on the fly from within construct 2 event pages.
you can download it from here http://tapcom.co.uk/plugins/GoogleMap.zip
I have compiled it with XDK and got a working apk from it and it works fab with the geolocation plugin. Not sure about any other IDKs. 'though.
Let me know if its useful to anyone??