Which of the following is not a warning sign indicating a Ponzi scheme?
The website of the Securities and Exchange Commission offers a seven-point list of things to watch out for that may indicate a Ponzi scheme, and "overly simple investment strategies" does not appear on that list. In fact, one of the things to watch out for is a secretive or complex investment strategy. According to the site, "Avoiding investments you don't understand or for which you can't get complete information is a good rule of thumb."
SOURCE: Ponzi Schemes – Frequently Asked Questions | U.S. Securities and Exchange Commission