Some members of the public could make an educated guess. Let's say you file a complaint about a stock. You'd do best to make it specific, with documentation and numbers. But you'd also do well to keep it fairly brief; you don't what whoever reads it just to groan and give up on it. So you say you'd be happy to discuss it, if they're interested, and give them your contact info.
If they get back to you with questions, and ask you to send more, then you're on the right track. If they call you more than once, you may be able to figure out what's going on by the questions they ask. They won't tell you anything, of course.
At some point, the company will be told that a formal investigation is taking place. If they're a reporting company, they're supposed to include that information in their 10-K.
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