Blue sky filing
Also called state notice filing, Form D state filing.
A blue sky filing is the notice, usually a copy of Form D with a state cover form and fee, that an issuer relying on Rule 506 submits to the securities regulator of each US state in which it has sold interests, because federal law pre-empts state registration of these securities but preserves each state's right to require notice and charge a fee.
Example
A fund's first close admits 14 LPs resident in six states. Form D goes to EDGAR on day 12. Counsel or a filing agent then submits a notice in each of the six states through the states' shared electronic filing system, each with its own fee and a deadline measured in days from the first sale to a resident of that state. A later close adds one LP in a seventh state, which starts a fresh clock for that state only. Two of the seven require a renewal or amendment while the offering continues; the rest are one-time filings.
Confused with
Form D. The federal notice. Blue sky filings are the state echoes of it, and most states accept the Form D itself as the substance of the notice.
State investment adviser registration. Blue sky filings concern the fund's offering of interests. Whether the manager must register or notice-file as an adviser in its home state is a separate question under the state's adviser rules.
In practice
The filings are mechanical and the deadlines are short, so they are missed when nobody owns the investor register by state. The fix is a column for state of residence at subscription and a filing checklist tied to each close. Fees are modest per state but add up for a fund with LPs across many of them, and a missed filing can mean late fees or a consent order in a strict state.