Doctor Strange: 31 Easter Eggs & References You Must See
25. The Book And Seal Of Vishanti
Obviously artefacts play a big part in the Doctor Strange universe; items come empowered with mystical importance even more frequently than people actually do.
One of the most important in the film and in the comics is the seal of the Vishanti, which is the symbol that emblazons the side of the Sanctum in New York and covers the Eye Of Agamotto. It comes with a book too - the Book Of Vishanti, which is "off limits" to Strange unless he steals it from the bungling Wong, which takes all of a few seconds.
In the comics The Vishanti are a trio of benevolent Gods from the multiverse, imbued with vast power who pass on power to those they deem worthy, like the Ancient One (and elsewhere The Aged Genghis and the Sorceror Supreme himself). Agamotto was himself appointed by the Vishanti before ascending to become one of them.
The other two are Oshtur and Hoggoth, and it was quite strange that Strange didn't utter his immortal line "by the hoary hosts of Hoggoth" - but I suppose that could only come after he actually learns about them a bit more.