Why are there red inverted triangles on the glass of Japanese houses?

Many buildings in Japan have red inverted triangle signs on their windows.

This sign is "Fire Brigade Entrance Sign". In case of fire and other emergencies, firefighters can enter the room from this entrance to search and rescue internal personnel.

The setting of the fire brigade entrance conforms to the sixth item of Article 126 of the Implementation Order of Japanese Building Standards Law. Buildings below 3 1 m and above three floors must be equipped with fire brigade entrances.

Meanwhile, according toNo. 183 1 of Japanese Ministry of Construction Announcement 1970, the sign of emergency entrance must be a regular triangle with a side length of 20cm and painted with red reflective paint.

Although there are many cases of sticking it into an inverted triangle, there is no requirement for sticking the triangle (positive and negative) in government regulations.