"The Royal Bank of Scotland has advised clients to take out protection against the risk of a sovereign default by China as one of its top trade trades for 2011. This is a new twist."

One red flag is the vast number of vacant homes spread through China, by some estimates up to 64 million vacant homes.

We've tracked down satellite photos of these unnerving places, based on a report from Forensic Asia Limited. They call it a clear sign of a bubble: "There's city after city full of empty streets and vast government buildings, some in the most inhospitable locations. It is the modern equivalent of building pyramids. With 20 new cities being built every year, we hope to be able to expand our list going forward."