What's a tip off to something being composite?

怎么能确定什么东西是合成的呢？

耶鲁公开课 - 死亡课程节选

You might ask though,is there some other behavior, something else that should tip us off,could tip us off, as to whether or not we really do or don't believe that we're going to die?

你可能会问，有没有其他行为，能够让我们突然醒悟，知道我们真正是否相信自己会死呢？

耶鲁公开课 - 死亡课程节选

It also allows it to tip off users to traffic jams, road construction and other obstacles.

FORBES: A Crowd-Sourced Navigation Service

Nott believes the paper was unwilling to tip off the public to the trick it was already using to obtain messages.

FORBES: Piers Morgan Attacks Critics, Calls Accuser Insane at Ethics Hearing

The newspaper says an emergency notice allegedly sent by authorities to tip off factories of upcoming undercover investigations by reporters is circulating online.

BBC: China media: Hacking denial