MDN: New rules banning decoration boards in vehicles set to come into force
Government regulations revised to totally ban decoration boards from being erected inside the windshields of cars, particularly large trucks, because they obstruct the sight of drivers, are set to come into force next month, officials said. The Land, Infrastructure and Transport Ministry on Thursday promulgated the amended ordinance to enforce the Road Trucking Vehicle Law. From Jan. 1, violators could face up to six months in prison or a 300,000-yen fine.
Critics have often pointed out that such decoration boards obstruct drivers' views and could trigger traffic accidents. Drivers of numerous large trucks have installed extravagant decoration boards inside their vehicles' windshields, each measuring 30 to 60 centimeters high. Such boards are made of stainless steel or acrylic acid resin and each of them is priced at 10,000 yen or more.

Arrrg, the translation of "decoration boards" is krazy.
They're called windshield shades or decorative shades.
(windscreen shades in the UK?)

Only decorations INSIDE the windshield? Well, that's okay and leaves plenty of "deko" to go outside.