Keep in mind it is a " tops optional " deck. It's open to the public, not just someone who wishes to have a private deck to sunbathe topless.
The only things supposedly banned are kids under 18 and cameras.
There may be a gawker or two, but as said it's public so if you want to go toples, you must expect that someone may see you.
If that bothers you, would suggest keeping 'em covered.