The stocks of oil drilling companies are in decline, falling alongside oil prices in a signal that some traders believe prices have further to fall yet. Since the start of the year, the stocks of the four largest onshore drilling companies have shed an average of 32%, the Wall Street Journal reported today. That’s a lot more than the decline of the energy sector of the S&P 500, which amounted to 8.2%, not to mention the broader index, which has gained 15%. The rig count in the United States has also, unsurprisingly, been falling, reflecting…