MIC is a way of indicating that a dispenser is in its original packaging consisting of a cellophane bag.
MIC is an acronym for Mint In Cellophane (or just "Mint in cello"). It is a way of not only indicating the type of packaging in which the dispenser can be found (in a cellophane bag), but also the condition of the dispenser (mint).
Cellophane bags were used for early Pez dispensers, prior to the 1980's and were sometimes stapled at the top to a card. When not affixed to a card the vast majority used a heat-seal but some very early examples used a simple twist closure. This type of packaging is distinguished by its usually brittle texture and plain appearance (no printing on the plastic itself). These should not be confused with more modern bagged dispensers (known as Mint In Bag) which use a different type of plastic and are brightly colored.