Set map marker as font icons in listing settings -> map settings -> map markers and info-window “Type of Map Markers” as Font Awesome icons (recommended).
Also you can set custom markers which includes as Image PNG Icons. while you submit ad after address field you can see select marker icon.
Now if custom icon not selected on submit listing category icon will be show.
To set Map Marker please follow the below mentioned Images:
Listing > Listings Categories > Select marker > Marker Color
If you will select PNG images then follow the Image 3.
Click on post your ad > Select Marker Icon > As in image 4.