If you place a control (or indicator) on a tab with the mouse, it'll be part of the tab. To "float" it on top of the tab control, place it outside the tab, then use the arrow keys to position it. You may need to "Move to Front" (CTRL+Shift+K) so that it will be on top of the tab. You'll have a shadow around the control in edit mode, but this will disappear when you run. I've used this trick when I want a control to appear on multiple tabs.
If you want to control it's visibility, use a property node.
Hope this helps
Tim