茶叶蛋, lit. “tea leaf egg,” or just “tea egg,” is a common type of street food in China consisting of eggs soaked for a long time with tea leaves and soy sauce. The shells are cracked to give the egg inside a marbled appearance.
My grandma once told me that another Chinese lady once told her that the most proper way to make these is to just use tea, without even adding any soy sauce. But pretty much every marinated egg I’ve ever eaten (whether with tea leaves or not) has included soy sauce. Actually, most Chinese food probably includes soy sauce.