Like in the comics, the MCU’s Sanctum is located at 177A Bleecker Street, and since Tony is looking southeast, that means that he’s looking in the direction of the Williamsburg Bridge.
So not only can Tony barely see anything in the distance from where he’s positioned on the street, more importantly, he’s not even looking in the same direction as where the ring probably is floating.
The Avengers: Infinity War trailer was also cut to make it look like Tony Stark was looking up at the ring while he’s hanging out with Bruce Banner, Doctor Strange and Wong near the Sanctum Sanctorum.
However, it turns out that whatever Tony is shocked to see, it’s not the ring.