When creating a custom brand (by copying an existing brand and modifying it), also make a copy of the <Customerconfigurations>/analyst/theme/banner/default/images folder, which contains the locator marker PNG file.
To change the locator marker, create a new PNG image with the same name, and then replace the existing image with the new one. The PNG image must be 32px x 32px in size and should have a transparent background.
Ensure the base of the locator icon points to the bottom middle of the image. The following example shows an icon that as 16px across and 32px in height.