A 100 bitcoin bar would have a face value of ~$95,000.  Given that much money at stake, I would require proof that the hologram sticker hadn't been tampered with...  I don't understand why anyone would have that level of confidence in such flimsey security.  It has been demonstrated that Casascius holograms, while tamper-resistent, are not tamper-proof.  $95,000 is a pretty big incentive for a lot of thieves.