This tag is used to label illustrations about Mami's cute side. Any chibi Mami related illustrations can be attached using this tag.
One thing about this tag is that most of the time, it uses Hiragana writing for it. There are cases where the Katakana version of it is used as well (マミこれかわいい). Since both tags work the same way, you are free to choose which suits best to your liking.