Matthew 24:30
The NASV, NIV really missed the Greek order of words.
In this case, the KJV correctly follows the exact Greek order.
"A token", indication, from Vine. The fulfilment of Matt 24 as a "sign" that Jesus (the messiah) was in heaven. cf. Matthew 24:34.
NOT a sign in the SKY (Jer. 10:2-3) such are worthless, cf Jer. NIV
The misunderstanding comes from a supposed vision by Constatine who saw a "cross" in the sky, and legalized Christianity. Many try to translate this verse to make it apply to that event.