Berkowitz doesn't own common stock which is why he states that he doesn't own common stock publicly.
This was written January 30th, 2017
We are frequently asked (i) why we own the preferred stock of Fannie Mae and Freddie Mac INSTEAD of common shares, and (ii) how this story ends. Our answers are simple: the provisions of the preferred stock contracts that we own provide us with greater security and certainty than the common stock and, as you know, we are not speculators.