A mystic veil protecting many mages to varying degrees from being located or spied upon. It can also be found on places & objects with mystic significance. It is a Background in all editions of Mage.
2nd Edition demonstrated the Mage Classic approach to Arcane over 5. Pg. 127 of Isle of the Mighty has a mage named Michael Scot with an Arcane of 7. Other mages, even those who were close to him, can’t notice him. He lives in a Chantry with his former friends but they believe his room is empty and kept that way as a memorial to him. He must succeed on a Willpower roll to be noticed. Mage Modern has a different view on Arcane over 5. Pg. 39 of Lost Paths states it is “accessible only to the Ahl-i-Batin”. High levels of Arcane separate a mage from the universe and lead to an end to the mage. The mage forgets his own existence as his body fades in and out of the Tellurian.