Sign of the Door by SUNGCHUL BAE from korea

The door is a passage for people to come in and out.
Opaque hinged doors are widely used in offices, classrooms and
other public facilities.
However, people might bump against each other in a crowded place
when they use the door at the same time on the opposite direction.
Such accidents frighten or even injure people.
LED light sign of the door can prevent people from bumping against
each other when they come in and out through an opaque hinged door.