I worked for a company (2009-10) that made big spinny ones for outdoor advertising (they got a few deployed in the UK) and were working on a 8'x5' billboard-sty

I worked for a company (2009-10) that made big spinny ones for outdoor advertising (they got a few deployed in the UK) and were working on a 8'x5' billboard-style one which had 8 huge rotors, each with 4 arms, coated in (of the time huge) LEDs. When it span up, it sounded like a steam-powered 747 trying to take off. Thankfully (because the potential for catastrophic disintegration was huge) the company went bust before any of these got deployed anywhere near the public.