On the case of Marks...

A mark is what makes a Magus, a Magus. It supplies them with their magical abilities and it enhances their physical abilities. People born without marks are called the Markless, they are just normal people. A Mark can give it's user anything, from the ability to turn into a frog to the ability to summon columns of fire.

The true power of a mark resides in the spirit that lives inside. If a Magus is strong enough, he or she can communicate with that spirit. The spirit has the power to detect the presence of other Magus, via their spirits. If a Magus is extremely strong, then he or she can manifest the spirit into the real world through a process called partial manifestation. In this state, the users body partial morphs into the spirit's body and his or her Magus powers will be increased dramatically.