In Greek tradition, both Archangels, not just Michael, are known as Taxiarchoi (Commanders) of the heavenly hosts, therefore, it is not uncommon to see Gabriel dressed as a warrior, as well as Michael. It is also the norm across traditions to see archangels (including Michael) robed as heavenly messengers, bearing an emissary's staff (often mistaken for a spear - it is not). The colors of their robes vary widely, though a common iconographic technique is to reverse the main colors for each archangel if both are depicted in the icon or deesis series. So, for example, one will be wearing a blue tunic under a green cloak, the other a green tunic over a blue cloak.
The surest way of identifying any archangel is to look at the inscription of his name.