I thought that this would be fun to add into for your post this is straight from Elias Encyclopedia First Edition Page 113:

" The 2-Factor Storage Bar uses complex two factor authentication to access the stored BTC value once it is sent to the bar.
these bars have their public address laser printed onto them, as well as 'casascius.com/2factor' which explains how the bars work.

In order to redeem the bar, on emust not only tear the hologram to retrieve the private key, but combine it with another code provided at purchase.
If a 2-Factor bar is sold, the seller will have the other part of the code, but is not able to access the funds as long as the hologram is intact.

For an unknown reason, all the first-bits appear to be intentionally obscured by black pen markings"