SEC Filings
Schedule 13D
Mandatory disclosure when crossing the 5% ownership threshold in a listed company with activist intent.
Anyone acquiring more than 5% of the outstanding shares of a US-listed company with the intent to influence the business must file a Schedule 13D with the SEC within ten calendar days. The filing describes the buyer, the source of funds and — most importantly — the intended actions (Item 4: "Purpose of Transaction").
A 13D is always a strong market signal because it typically flags an activist and frequently produces sharp short-term price reactions. Investors with no activist intent file a Schedule 13G instead.