In Chinese culture, this is rather common(I've lived in Singapore and I saw a lot of this)!

It's like a pun. In Chinese, if you say "福到了“, which says "fú dào le", it means "Fortune is here". On the other hand, if you say "福倒了“, which also says "fú dào le", it means "Fortune is upside down/福(character for fortune) is upside down". But since it sounds like "福到了"- "Fortune is here", many Chinese people put up 福 upside down to symbolise "Fortune is at their house"!



Sorry @/Ry-Sprit if I stole your comment XD