If some of the smartest guys in the market are selling, investors should ask themselves whether this is really the best time to buy.
After 36 years as a private company, commodity trading giant Glencore is going public with listings in London and Hong Kong. In what is set to become the biggest initial public offering of the year, the company is expected to raise as much as US$11 billion in a deal that will net its senior executives billions of US dollars each.
With trading operations in commodities as diverse as aluminium and barley, and mining interests from the Congo to Kazakhstan, Glencore shares have been touted as the ideal way for investors to play the structural bull market in commodities driven by surging demand from developing Asia and China in particular.
Yet beneath the excitement there lurks a nagging doubt. Some investors are wondering why, if commodities are such a compelling story, Glencore's current owners are so keen to cut their exposure to the business by going public.
Perhaps, reason the more sceptical, Glencore's bosses know something we don't. Perhaps they don't share the widely held belief in the sustainability of the commodity bull market and are selling while they still can.
If so, this would not be the first time that the flotation of a successful privately-held company has signalled a market top in its sector.