Stamps are still widely used, but these particular postcards ask for a handwritten signature. I suspect that the choice was made to require signatures rather than stamps not because forged signatures are easier to catch but because family members would be more hesitant to forge a signature than to use a dead person’s stamp. Using someone else’s stamp is not unusual and can be innocuous: often office workers, for example, will stamp documents on behalf of their bosses using their bosses’ personal stamps. Forging a handwritten signature is more likely to feel like a crime to many Japanese.

I forgot to mention that one of the Japanese insurance companies also requires short face-to-face interviews every few years. I have done it once so far. They wanted to do it in person, but it was during a COVID spike and they let me do it by videoconferencing instead.