The invention features an apparatus for delivering mechanical energy to an expanse of skin, wherein the apparatus includes: (a) a skin-contactable element having a skin contactable surface; (b) a motor; and (c) a transfer member for transferring mechanical energy from the motor to the skin-contactable element in order to provide periodic motion to the skin-contactable surface; wherein the skin-contactable element includes a signaling marker that is adapted to provide a change in a sensation that is discernable to a user after a period of time of operation of the apparatus, and wherein the sensation is selected from a group consisting of tactile, olfactory, thermal, visual, auditory, and combinations thereof.