YSK in an incident involving a casualty in public with a lot of people around, help them watch over their wallet and phone or any valuables they are wearing, or confirm it with the person they are with.
from /r/YouShouldKnow
YSK在涉及傷員的事件中，在周圍有很多人的情況下，幫助他們看管好自己的錢包和手機或他們所佩戴的任何貴重物品，或與他們在一起的人確認。