[piaste]

My current phone (Xiaomi POCO F2 Pro) only displays a faint lock/unlock icon above the logo while booting. Easy to miss.

But that's not really important, because unlocking the bootloader factory resets the device on every Android phone that I know of. AFAIK it's not possible to unlock a bootloader without the owner's knowledge.

[causi]

Even if it's easy to miss, a person like Snowden would be looking out for it.