Indeed, the sec and the company probably want to know about you, hence the 13D. There's also a bit where you can only hold a certain portion of a bank before being designated a bank-holding company.

I don't know what scrutiny that brings, but Warren Buffett has been careful not to get Berkshire Hathaway designated it. I believe the limit is/was 10%, but then you could ask the Federal Reserve for a higher limit, which they did because of Bank of America or Wells Fargo I believe? I don't know a tremendous amount about it, but from what Buffett was describing, it wasn't the fed asking them about their bank holdings, they were asking the bank about them.