A suitability doctrine first introduced by the Securities and Exchange Commission in the 1930s. The idea is that a broker who hangs out a shingle will represent his or her customers fairly and responsibly when making suggestions regarding securities.
Investopedia Says:
Also referred to as "fiduciary duty", these suitability doctrines were originally used to ensure the protection of investors from unscrupulous broker-dealers.
Here, "shingle" refers to a small sign, indicating a professional office.
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Find out how this regulatory body protects the rights of investors. Policing The Securities Market: An Overview Of The SEC
The better you understand why insider trading can be criminal, the better you'll understand how the market works. Defining Illegal Insider Trading
