There are many reasons that insiders sell, eg: taxes. diversification etal. Does not necessarily mean bad news is on the forefront. On the flipside however, the only reason insiders buy...is to make money and they feel the stock is undervalued.
companies usually have a General Counsel, who oversees executives' stock trades...usually knowledgable of SEC regs, rules, procedures, "do's & don't's", "no-no's" to insure trading is done above board or on a schedule (planned sales) to avoid even the appearance of impropriety or insider trading. But, it's just based on my very limited knowledge of securities law. There are windows that open & close at public companies, allowing trades even by executives.