Removing the Chinese text "未写入google key和tee key" watermark on the screen

After flashing a custom ROM, there is a watermark in the top-right of the screen saying > > > 未写入google key和tee key I've googled it and have tried several of the solutions suggested, but none have worked. Interestingly, most people get a slightly different variation of this message, in red. I've removed "FactoryTest" from my phone, but do not have com.mediatek.factorymode as some have suggested. I've messed around with my IMEI keys, this did not help. The message also still appears even with the SIM card removed. Where on the phone could this be stored? My phone is rooted, so if I could locate the file responsible, I could easily delete it.