Sevens are a massive number in Chinese numerology: The 7 parts (yin/yang/metals), the 7 steps, 7 captures, etc.
Eights are symbols of prosperity, wealth, generosity, good fortune in business, etc.
Six is a kinda useless number for money -- Smoothness and whatnot are less for money and more for one's tongue. You'd name a wine after a six (I've seen "Dice Wine" referring to 6-sided dice) but not look for it in bills
Well, https://hsbc.banklocationmaps.com/en/chn/shanghai only lists one branch at a street address of 666, and that one is really just sharing the address of the commercial center where it's located, but that still seems like enough for this point.
8 is heavily represented. 6 is a runner-up. 7 doesn't appear to be significant in this context.
Consider the branch phone numbers:
3888 3888
3888 8468
3888 8900
3888 1200
6279 8582
3888 3111
3888 1318
3888 1188
3888 6455
3888 8618
3888 8688
3888 1218
3888 6388
There is technically one 7 in there, but it seems clear that the bank would have preferred not to have it. Counting only the second halves, 8 is overwhelmingly popular, so is 1 (for reasons I don't know), 6 is only barely ahead of what's typical, but still in third place, and 7 doesn't even exist.
For those who are interested: the Chinese character for 8 is a pair of downward lines, close together at the top, far apart at the bottom. Looks a bit like / \. The idea behind it, as far as I know, is that it represents things growing larger, which is why it is of interest where wealth is concerned.
Eights are symbols of prosperity, wealth, generosity, good fortune in business, etc.
Six is a kinda useless number for money -- Smoothness and whatnot are less for money and more for one's tongue. You'd name a wine after a six (I've seen "Dice Wine" referring to 6-sided dice) but not look for it in bills