How to check BOOTLOADER lock/unlock state

[Support]

[Lock] bootloader state:
factory signed firmware installed: bootscreen says nothing
modified firmware installed: bootscreen says [Red State] and Device can not boot.

[Unlock] bootloader state:
bootscreen says [Orange State] or [UNLOCK] or something like that and Device can boot after short delay.

Right after [Unlock => Lock] or [Lock => Unlock] state change userdata will be erased.