サングァー (kanji: 魔除け) sangwa
Sangwa is an Okinawan protection amulet or talisman, like a type of omamori お守り, that is made from susuki leaves in a cross-shape. It is a charm to protect offerings, food, and children from majimun マジムン (evil spirits). Sometimes they are put on houses or in lunch boxes (bento 弁当).
The pizza company Pizza Paruko パルコ has this symbol on their takeout pizza box. Be sure to look for it!
You can also purchase small keychains made of leather or other materials in the shape of sangwa at some of the small local shops.
You may also see something like this during certain times of year, such as 8th Lunar month in Okinawa: ハチグヮチ (八月) or other celebrations where talismans are used.