If somebody else picks up your phone and sees this app it will just look like a regular note-keeping app. But they are actually seeing a bunch of bogus notes. Draw any squiggle to make the unlock screen show. When you enter the correct unlock pattern the bogus notes are hidden and your real notes are displayed.

To be sneaky the app isn't called "secret" or "secure" notes. And there is no safe or lock in the icon.
Optionally, Snotes can even automatically maintain dates on your bogus notes to make them appear current ;)

This is the Paid version:
+ no ads
+ unlimited secure notes