I'm looking at a picture of the electrical panel of a Phenom 100 and on it I see a + sign, does anyone have any ideas as to what it's supposed to mean?
Above I marked five similar plus signs on the 737 (there are more). Beneath the +'s are the contacts for the backlighting of each panel. If it acts up then pressing on the sign will ground/secure the connection and may solve the issue.
The electroluminescent light-panels are flexible and the ride can be too bumpy sometimes. Better push the right spot than wait for a specialized someone on the ground who knows where each contact is.
Composite based on images from b737.org.uk.