In Japan, there are various ways to sign legal documents. Although many companies now a days allow foreigners to use western-style signatures. For legal purposes, since the Meiji Era (1868-1912) most Japanese use a stamp with their family name.
The tool of the stamp is called the hanko. And the imprinted image is called an inkan.
There are three types of hanko. A jitsuin is used for legal contracts like buying a car or house, a ginkōin for bank transactions, and a mitomein for daily use.
Anyone over the age of 15 is allowed to have a hanko. Getting one it is quite simple. There are a number of shops which specialize in making them. Getting a custom hanko with no frills can be as cheap as 1000 yen!
Most foreigners choose to have their name written in katakana but Roman lettering is also acceptable.
mitomein are not registered and so they can be as simple or as fancy as you like.
To register a jitsuin you have to visit your municipal or ward office and and apply for the seal to be recognized. In this case you need to have an inkan which matches your official legal name as registered with the municipality. Since the hanko is thereafter legally binding, it should be kept safe to avoid identity theft.