Enrico:
You would not make them scale independent, you would use Model View Options to show them when desired. You should create 2 Model View Options, one with the Markers shown, the other with then hidden, then assign the appropriate MVO to the appropriate View.
For more information with images, go to Help > ArchiCAD Help, when your browser opens click on the "Search" tab, and input "Model View Options" in the search box, the results list will lead to detailed information.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David