If you're like me an interested in RFID but wouldnt quite be willing to implant a chip under your skin, this might be a nice alternative assuming it has RFID tech too. I'd love to have this tattoo and hack my front door to open via an RFID.
Once you have your key of identification implanted you just created a seriously disturbing incentive for someone (without a reader to clone your RFID) to do you grievous harm when they simply want to steal your stuff.
It probably won't happen to you or many other people but it's enough of a concern that I'll put up with the occasional misplaced key instead.
tl;dr I'd love to hack your tattoo and get in your front door.