How do I use the lamp?

[GotTheKittens]

So, I got that the lamp is supposed to help me make a decision, but all never see any +/- symbols, only ???? above all of them.

I bought everything there is to buy, what am I missing?

[nolifeprincess]

It's for second+ playthroughs, it shows the consequences of previously marked profiles. There seems to be a LOT of profiles so even in my second playthrough, I had a lot of question marks, but some would show +/- when I held the marker in my hand as well (not just having it under the lamp). Also you can see the results after marking live or die.