Or it means the CEO wants to buy a yacht.

Either way if you think it's such a strong signal about company's prospects, go ahead and short companies whose CEO are selling the stock.

CEO stock sale is public information. Disclosing those sales is mandated by FCC.

You have no excuse for not being very rich.

Alternatively, CEOs are selling stock for variety of reasons and you can't make judgements about the company with confidence greater than 50%. And lower confidence is basically a random coin toss.