This is 100% true.
John and I went to eat at a Chinese restaurant this afternoon. It looked and felt like any one in the U.S. The only differences were that they had sushi on the menu, and of course they spoke Spanish.
Everything was delicous. At the end of the meal, John had ice-cream and I had cafe solo. John asked for the check, and with it, the server brought 2 very small shot glasses with Chinese artistry painted on the outside. He filled them from a bottle and told us that it was sweet rice wine. They were tiny glasses, so we decided to try it. When we picked up the glasses, John said, "Hey, there is a picture at the bottom!"
We looked closer. It was of a man. Wearing a smile. And nothing else. And he seemed to be very happy about whatever he was smiling about. Very happy. I drank mine (it tasted like apple juice) and John's too. He said he did "not like the drink." I don't think it was the drink.
Anyway, when you drink the liquid, the bottom of the cup is rounded glass, so you can no longer see the picture. It is too distorted by the glass.
Intrigued all over again, we both filled our cups with water to see the picture come back up. No pun intended. I don't think we started laughing about it until we got all the way back to the car. It was sort of like, "Did we just see...? Yeah, we just saw....! Ok."
We cannot wait to try a different Chinese place to see if we get free "shots" at the end of our meal. John is hoping the pictures are of women next time.