You can protect your RainbowNote from other people to set passcode. To enable passcode option, from Note List page, touch gear icon then touch "Passcode Lock".
In "Lock Settings", touch "Passcode Lock" button. After reading description, touch "Enable Passcode Lock".
You can enter 4 digits as your passcode.
If you forget your passcode, RainbowNote can send your passcode to your Google Docs.
So don't forget to set your Google ID and password. To set your Google ID, open "Settings" -> "Google Settings".