Use of a hanko implies that you're acting on behalf of the owner of that hanko. If someone signs a paper with your name, you can say someone forged your signatu

Use of a hanko implies that you're acting on behalf of the owner of that hanko. If someone signs a paper with your name, you can say someone forged your signature and prove that your writing is different. If someone fraudulently uses your info digitally, you can get them to pull up IP records and other various digital fingerprinting info to prove it's not yours. If your name is stamped, you're kind of boned. It's not an uncommon thing for people in Japan to be divorced without even knowing it. Their spouse secretly grabs their hanko for 5 seconds to do a quick stamp, goes to the city office alone, hands in the divorce form with both names stamped, and it's finalized. There's actually a separate form called a fujuri todoke that you can do in advance to block these one-sided divorces, showing that the whole stamping system is flawed if you need to do separate forms to block potential events of it being used without your knowledge. Nearly anything works better than stamps.