maternity mark

A charm or button badge given to women in Japan at their first checkup after getting pregnant. It is so they can prove they are pregnant before it shows in order to use the priority seats on public transit or cut to the front of a line. Also found on stickers to place on cars, much like the "baby on board" sign in the US. It is sometimes called the "baby inside me" mark in English.

It reads:
おなかに赤ちゃんがいます
Onaka ni Akachan ga imasu
In (my) belly is a baby

Example

A typical maternity mark design