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在涉及伤员的事件中，在周围有很多人的情况下，帮助他们看管好自己的钱包和手机或他们所佩戴的任何贵重物品，或与他们在一起的人确认。