stickers

See the following from Do not use palm rest or keycap covers on a Mac notebook with a Retina display - Apple Support

Leaving any material on the top case (keyboard and palm rest area) could result in damage to the display when you close it.

To enable the thin design of Mac notebook computers with a Retina display, the clearance between the display and the top case is engineered to tight tolerances. Do not use palm rest covers or keycap covers, as the additional thickness may interfere with the designed closed position of the display.