ACF Map Markers
The marker is the image that identify the position on the map
You can handle it in a static way, equal to every marker:
ACF FIELD Image Marker
Or you can use a customized ACF Image Field set to the post in addition of the GoogleMap Field.
The metabox in the management of the single post.
NOTE: If you don't specify any custom image the marker will be the default from Google Maps.