Other mistake: The shot of the fleet outside of the barrier is reversed. The Aircraft carriers landing deck is slanted right instead of left. (01:15:00)
Other mistake: When Alex Hopper is being tasered and arrested for robbing the convenience store, you can see his shirt is almost clean on his back. But he fell on the bottles and sodas rack in the store, the shirt should have stains.
Other mistake: Early in the movie, It is said in the movie that the force field is 300,000ft in altitude, and approximately 2 miles in diameter. It is far less than 300,000ft high, and larger than 2 miles wide.
Other mistake: When they load the last shell to hit the island Hopper orders it to be taken from turret 3 to turret 2, but turret 3 is later seen firing.
Answer: They appear to be versions of a Hawaiian lei. During ceremonies and celebrations, it is permissible to wear pins, ribbons, and other items as a show of respect or support.