Please note: The following is from the release notes of Notes 8.5.2 so I don’t take credit for writing this. Lotus Notes 8.5.2 is in beta and there are no guarantees that the features described here will be in the final product that IBM ships.
Power users and administrators can add a new viewImageUrl attribute to the palleteItem element in a widget’s extension.xml definition to specify a custom icon to use in the sidebar view/title bar for that widget. The viewImageURL attribute value must be a URL to the desired image, for example:
Example widget XML syntax is shown below: