On 3/3/2021 at 8:59 AM, liuzhou said:I'll have a closer look next time I pass KFC, if the poster is still there.
OK. Solved the question.
What looks like olives could hardly be more different. It is either Chinese black fungus (aka black wood ear fungus) 黑木耳 (hēi mù ěr). Auricularia auricula-judae, or kelp (seaweed), 海带 (hǎi dài). Saccharina japonica ; in Japanese 真昆布 or kombu.
Given it is with seafood, I'm going with the latter, but can't be at all sure.
Here is a close-up of the poster.