The LHS  .. USA Drivers side .. top of dash contains the Vehicle Identification Number.. the slot opening .. originally had one of these often perished and just missing now surrounds.. probably to help center the visual of the number and stop crap going over the VIN.

USED specifically on GM 68-72 A body

GTO, Lemans, Skylark, GS, Cutlass, Chevelle & the 68-72 El Camino