After flashing a custom ROM, I now have a watermark at the top right of my screen (screenshot attached). I googled it and tried several of the suggested solutions, but none worked. Interestingly, most people get a slightly different variation of this message, in red …
I have removed "FactoryTest" from my phone, but I did not mediatek.factorymode as some have suggested.
I played with my IMEI keys, it didn't help. The message also always appears even with the SIM card removed.
Where on the phone could it be stored? My phone is rooted, so if I could locate the responsible file, I could easily delete it.