I have no doubt the SEC has a bunch of rules they use to flag suspicious transactions. The data analysis spits out a few names and they follow up in person to see who lawyers up and who cracks under pressure.
It's also why Matt Levine's "rules of insider trading" includes "Don’t do it by buying short-dated out-of-the-money call options on merger targets".
Certain transactions are suspicious as hell, especially when they can look at your trading history and determine you've never really traded much and just opened the account 2 days prior and made a $100,000 bet on the trade. Or for the really clever people, they find out although you made a suspicious trade you don't work for Amazon, but LinkedIn says you're the wife of someone who works in finance there. Oops!
Though I wonder if that rule needs to be updated with r/WSB doing these trades all the time.
https://www.bloomberg.com/opinion/articles/2018-08-12/the-10...