Greetings
These Marks are called mass point if you press it provides a ground contact enabling current to flow thus the back light to come ON in case of faulty switch, i.e all panel is lighted except one plate, then press the + of that plate.
but to me the most important is why the upper panel has two colors Dark grey and light grey, it highlights systems affected by the Fire Switch
no no no..
pappy j
says it for checking airframe rigging due to when it flys it bends and doesnt return back to its normal design.
that is quite funny, the thought of checking airframe rigging in the flight deck against the panels.
