Lowercase F written on motherboard

Hey guys,

I’ve got a Switch off of ebay for cheap and wanted to see if I could fix it. This one clearly has some corrosion going on, so maybe it just needs a cleaning, idk yet. Anyway, there is a lower case F written on it with marker or something like that. Has anyone seen something like this before or knows what it means? Not sure if it has already been opened before, I kinda doubt it since I bought it in a bundle with a bunch of stuff including the retail box etc.

Here’s an image:
imgur. com/a/XZkZReJ

the picture link does not open in the browser

Yeah sorry, you need to remove the space between the . and com… It didn’t let me post a link for some reason…

Probably the console was opened and the one who did this, wrote with the marker a “F” from “Faulty”.