Like its name suggests, unconventional marketing encompasses a large group of marketing practices which are considered as non conventional. Unconventional marketing is therefore a very subjective term.
Unconventional marketing includes really unconventional practices or techniques and some "traditional" marketing techniques which are used through unconventional ways.
Traditional marketing techniques which can become unconventional by the way they are used through "out of the box thinking":
event OOH advertising
Unconventional marketing is often seen as a synonym of guerilla marketing.
Some examples of unconventional marketing with OOH advertising: