In iOS 9.3, you now have the ability to protect notes created in the Notes App.
To turn on the password feature, tap Settings > Notes > Password.
You will the be prompted to enter a password. You can also use Touch ID on devices with this feature. If you forget your password, you will not be able to view your locked notes.
Locking your notes keeps them private from others who might use your Mac or iOS device. Notes uses a single password to lock all your notes (both notes in your iCloud account and notes stored on your device).
When you create a password for the notes on one device, all other devices that use the same iCloud account use that password too.