First is during Georgi's Free Skate in episode 7, when he's thinking about Anya. There's a photo on her Instagram of matching rings with her new guy.
(Poor Georgi! ♥)
Second and third are both in episode 10. When Yuuri wakes up from his nap, he scrolls through his Insta feed and sees JJ and Isabella showing off their matching rings. He looks at that photo longer than you'd expect! Almost as if it's given him an idea...
And then, of course, THE rings.
I still remember with glee how masterfully the episode preview trolled us with Yuuri saying he was going to give Victor something "round and golden".
I love YOI's attention to detail and callbacks. And all the light flares on those rings.