Zooming should occur instantaneously, so that seeing the content change size provides mobile device users with all the feedback they need. Therefore, a zoom indicator is usually not needed.
However, application developers can provide users with a zoom indicator to help users determine the current zoom level. For instance, if three text sizes are defined and the largest is already in use, it is good to see an indicator when trying to zoom in. The indicator should be a floating component that disappears after a short time-out.