Apparently so, although it seems to have a separate history and meaning from other historical uses. From Wikipedia:
Since ancient times in Japan, the heart symbol has been called Inome (猪目), meaning the eye of a wild boar, and it has the meaning of warding off evil spirits. The decorations are used to decorate Shinto shrines, Buddhist temples, castles, and weapons.
Were hearts a symbol even back in ancient japan? Didn’t know they were around for so long
Apparently so, although it seems to have a separate history and meaning from other historical uses. From Wikipedia:
https://en.wikipedia.org/wiki/Heart_symbol