CaPattinson Chris,
There are many thousands of registered TP members - but most of those thousands don't post but can still read anything on TP if they bother to log in.
There are also many many registered TP members who have never ever posted, but can still read anything on TP and that includes the Tea Room if they bother to log in.
So unless you hire a private detective to trawl through each of the registered members, and then to gain access to all the information about them that is held securely by the Alz Soc, you may never know who is reading whatever you might wish them not to read.
The message of that all? If you don't want 'someone' to read 'it', then you should be well advised by the TP moderators that you don't post it on the internet.