you can pass the parameter dialog.setPreference('sysparm_draw_only', 'true'); in your UI action or script that is calling the dailog. 

    var dialog = new GlideModal("accept_signature"); //Instantiate the dialog containing the UI Page 'add_comments_dialog'
    dialog.setTitle("Sign the incident"); //Set the dialog title
    //dialog.setPreference('sysparm_draw_only', 'true');
    dialog.setPreference("sysparm_document_id", sysid); //Pass the comments into the dialog
    dialog.setPreference("sysparm_table_name", table); //Pass in a short description for use in the dialog
    dialog.render();