As you guys can see, the piece actually centers on the round window displaying the symbol also seen in Stephen Strange's mystical amulet, the Eye of Agamotto, which may or may not be the Time Stone. Have a closer look at the amulet above, then check out the concept art below:
As a bonus, executive producer Louis D'Esposito also tweeted an actual set photo offering a nifty close-up at the same window seen in the concept art, revealing how close to said original concept art the set is; although the actual window is much muuuuch more detailed than what was originally conceived. Isn't that window a beauty? Just look at that craftsmanship:
Long story short, Doctor Strange centers on Dr. Stephen Strange (Cumberbatch), a brilliant but arrogant neurosurgeon who discovers a hidden world of magic and alternate dimensions in the wake of a near-fatal car accident that cripples his hands.
Directed by Scott Derrickson (Deliver Us From Evil) the movie stars Benedict Cumberbatch, Tilda Swinton, Chiwitel Ejiofor, Mads Mikkelsen and will open on Nov. 4, 2016.
(via Comic Book Resources)