If your device supports Apple Touch ID, you can activate this to give added protection to your SigFig app. If you go to the "Settings" window on your app (contained in the icon in the bottom left of your main page), you will see a switch turn your Security Pin on and Off.
To enable Touch ID, just make sure that this switch is turned ON and your Touch ID is active on your apple device.
When both of these are active, you will be prompted to use your Touch ID when opening your SigFig app.
Let us know if you have issues getting this set up at firstname.lastname@example.org