elements 9 layer mask thumbnail does not appear

Layer masking is not working for me. When I select the layer mask button on the overlay layer I do not see the white box appear in the layer. I am using an overlay layer on the top of background layer. I do have selection in this overlay layer. Subsequently when I try to paint brush in this layer nothing happens. Would I need overlay layer for the layer mask to work?

Any suggestion is appreciated.

-Joydeep