Thumbprint as signature y/n?

July 23, 2009 2:02 AM

Pros & Cons of using thumbprint as signature?

My bank here in Japan recently gave me a lot of trouble over my signature which they claimed didn't look exactly the same as the one they had scanned into the system (although it's plainly the same one on my passport). Really though I'm not particularly attached to my signature, but I can't use a hanko (stamp) on my Australian documents (or technically legally my Japanese ones as I did not register under my husbands name and can't use his hanko or the unregistered one I do have).

I'm thinking I want to say bugger it all and use my thumbprint as my signature as it seems to me to really be the most secure authentification available.

What are the pros and cons about changing over from a signature to a thumbprint? Has anyone done it? What problems will arise?

Some context - I live here in Japan now but only my bank needs a signature. The other documentation is based on my Australian passport so that's probably where any issues are going to crop up.

posted by gomichild to law & government (12 comments total)

I've never done it, but it sounds interesting. Possible problems I can think of:

1. Would you need to use your thumbprint as your signature across all documents that might be used to support your identity? e.g. the passport that you mentioned, any credit cards etc. Will this cost you money, or time?
2. Will there be enough space for a thumbprint on any documents you have to sign? Signature spaces on some documents can be quite small.
3. Who or what is validating your print at the bank, and will that method be up to the task? I imagine computer imaging systems optimised for writing may not cope so well with prints, and it may also take humans a second extra glance or two to confirm a match.
4. If your signature needs to be scaled in a computer system, loss of fidelity in the print may make a match tricky (I've noticed that my signature has been scaled down on my UK passport).
5. Most importantly, what happens if you cut your thumb? Will you lose access to your account for a week while the wound heals? Worse, what if you lose your hand? :/

On balance, it may be more trouble than it's worth. It might be an idea to discuss with the bank manager though.
posted by raveturned at 2:19 AM on July 23

That's a good list of points raveturned - some I'd thought of (but not considered losing my hand!).

Currently with fingerprinting to enter several countries (and I think the Japanese govt are trying to bring back fingerprinting on gaijin cards) so it seems like a lot of places already have the ability to verify fingerprints.

With hand losing and injury surely this would apply to a regular signature too? If you have to sign with your other hand if you injure your writing hand you'd have the same issues so there must be some recourse for it.

As I discovered at my Japanese bank there is no way to verify signatures or hanko stamps short of someone just looking at them on a computer screen and then having a look at the version on paper.

Time and money to do so is a consideration but would also be if I changed my written signature too I guess.
posted by gomichild at 2:30 AM on July 23

...use my thumbprint as my signature as it seems to me to really be the most secure authentification available.

It's not. Or rather, if the world were set up to identify you (in signature situations) by your thumbprint, you'd be absolutely right. But, it's not.

The problem is that, except to an expert, one thumbprint looks pretty much like another.

Untrained people are reasonably decent at spotting mismatched signatures--e.g. casual forgeries. We're also tend to notice when somebody takes twenty seconds to sign 'their' name, carefully tracing what appears to be a casual hand.

But, if you're clerking a hotel, and I hand you a passport with print and then sign the bill with a print, are you really going to pull out your magnifying glass and identify corresponding whorls? Do you, gomichild, know how to identify matched (and more importantly, mismatched) prints? How about from a partial with smudges and streaks?

If we had computers automatically checking the matches, it might be one thing. But, as it stands, the only practical security advantage that comes from using your thumbprint is that somebody attempting to "forge" your print in front of somebody else is going to have to use their actual thumb. So, they're going to leave behind some identifiable evidence of their crime. Except, of course, that's not much use at all if the forger already has all your money and is on their way to Taiwan.

But, honestly, with probably 98% of the people who're going to see your new signature, you may as well use a blob of ink.
posted by Netzapper at 3:57 AM on July 23

Someone could chop off your thumb and use it to gain access to your stuff. (Probably unlikely, but something that's worried me about biometric IDs ever since I saw the movie Demolition Man...)
posted by LolaGeek at 5:22 AM on July 23

Seconding LolaGeek, except that I'd rather cut off my thumb than watch Demolition Man.
posted by box at 5:55 AM on July 23 [2 favorites]

Would you carry an ink pad with you?
posted by The corpse in the library at 7:12 AM on July 23

Do you, gomichild, know how to identify matched (and more importantly, mismatched) prints? How about from a partial with smudges and streaks?

Well why do they bother with all the times you do have to give your fingerprint? Are these just shows of false security? I guess this started because the person checking my signature was clearly not able to tell the English handwriting I was using.

Would you carry an ink pad with you?

Probably. It's a standard practice here in Japan anyway to carry one with your hanko so not such a foreign concept for me. Certainly I would if I had to deal with anything official - although there are usually ink pads available whenever you are expected to stamp something. This would obviously be different in exclusively signing countries.
posted by gomichild at 7:37 AM on July 23

The purpose of a signature is not authentication. They're easy to forge. Use whatever is convenient.

Related: Bruce Schneier on fax signatures
posted by qxntpqbbbqxl at 7:38 AM on July 23

Cons:

1. You might get hassled a little...and told to use a signature regardless of what they're comparing it against (fingerprint).

2. A smaller percentage of people will actually compare the two fingerprints...as compared to the people who check for a matching signature. You're actually making it easier to forge...just because less people will feel the need to be bothered to check whirls and whorls on your fingerprints.
posted by hal_c_on at 9:15 AM on July 23

Won't your finger frequently be inkstained?
posted by Jahaza at 7:07 PM on July 23

One thing to keep in mind is that only a hanko (or rather, a registered 実印) is accepted for some transactions, so you will inevitably end up needing one at some point. If I were you, I would carry an unregistered hanko for use when a signature won't cut it (or if you think you'd get grief by signing).

Either that, or change your bank. Neither Tokyo Mitsubishi, Sumitomo Mitsui, nor Shinsei have given me any trouble so far.
posted by armage at 12:43 AM on July 24

Actually it was Shinsei Bank giving me all the grief.
posted by gomichild at 3:27 AM on July 24