It's not just guessed PR, it is poorly guessed PR. If you aren't showing you probably have o pagerank. Geocities starts off at zero just like any other page, even if it looks cool to have that fake PR7 there.
When I created a new account a Geocities, I had PR7 straight away. Even my page is still showing that I aven't started my site yet. This MUST be an estimated PR. How else can you get this PR without even building a site? Go to google. Search for your URL. Go to your site (if you were listed) What you then see is your PR.