I'm going to point you in two directions at once so you can consider both options before selecting an approach to try:
See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis" for a description of how to set this up.
This method is a very secure way to limit access to entire records--your notes can be recorded in a related table and the above method can control who can see particular records in the notes table.
There are a number of ways that you can make a given layout object seem to appear/disappear from a layout: https://www.dropbox.com/s/8levaz6deiyzjr8/LayoutObjectVisibilityControlDemo.fp7
This method is much less secure, but possibly simpler to implement.
Thanks for your assistance PhilModjunk. I have been studying your suggestions and think the first method will be the approach I take. I will post back if I get stuck. Thanks again.