Thanks to a Redditor who snapped a photo of the order screen at the counter of popular dim sum spot Yank Sing's Stevenson Street operation, we see that restaurant workers have big buttons that say "ASIAN," "NON-ASIAN," and "CHILD" that they need to use when entering orders. But, as it turns out, this is just a casual demographic study being done by the manager, and not a system by which Asians get special discounts or something.
SF Weekly confirms with an employee there that no one gets any special discounts. The manager "just wants to keep track of what kind of people are eating here," we suppose so that he can understand how popular their dim sum is with various demos these days.
At least anecdotally, the customer base is said to be about a 50/50 split between Asians and non-Asians. But, as some of you may know, Yank Sing, while delicious, is kind of pricey, and there are many, many dim sum spots around town that are cheaper, some of which are noted in the Reddit comments. And, as one commenter jokes, with a tried and true riff on the restaurant's name, "Yanks sing for their supper while the Asians get it for a song."