When editing a map marker, I cannot use Alt + Enter to view the full list of pin icons. All it does is open and close the written list.
Edit a map marker, when choosing the pin, try using Alt + Enter to view the icon reference, as prompted by the (?) information popup.
sorry for a late response but we are currently working on a better version of the map markers list so the previous version currently unavailable - the text should be also gone to not mislead any users :)