hickey

A hickey, love bite, or slag tag is a bruise or mark caused by the kissing or sucking of the skin, usually on the neck or arm. The mark is created by the bursting of superficial small blood vessels under the skin.

It's sometimes called a "kiss mark", but this should not be confused with the lipstick mark tag. Also, apparently both lipstick marks and hickeys are tagged as キスマーク on Pixiv.