It might be a nice feature to be able, with a shortcode, to display all submitted markers for a particular user. I cannot find that there is any way to do that currently.
Thanks!
Unfortunately, marker data is stored to the map and does not contain any user data for who has added these markers, however, I will kindly take note of this suggestion for possible inclusion in a future update of WP Go Maps.
If we do decide to introduce user associated markers, this will likely be a feature we take into consideration.