SEC Filings
Form 4 (Insider Transaction)
Disclosure of securities transactions by insiders (directors, officers, 10% shareholders).
Form 4 must be filed within two business days by insiders — directors, officers and shareholders owning at least 10% — whenever they buy, sell or exercise options on their own company's stock. The data is treated as an important sentiment signal because insiders have the best view of the business.
Large insider sales are not necessarily a warning (often diversification or tax-driven), whereas cluster buys by multiple insiders at the same time have historically been a strong contrarian indicator against pessimistic market sentiment.