The default eye icon for an observer is configured in the default style file of the Observers layer. You can change this default style file through the TLcyLspShapeVisibilityFormatAddOn.observers.defaultStyleFile property in the configuration file of the TLcyLspShapeVisibilityFormatAddOn.

At runtime, you can change the icon style exposed by the ILspCustomizableStyler of the Observers layer.