Emojis on my bio?

MomOf2 • Married 💏 DD:4yrs old 👑 Angel Baby 5/6/2014 👼 My Rainbow Baby! 5/21/2015 👶🍼💙
I was just wondering why do the emojis turn into '?' after I apply them to my bio? Can they still be viewed or are emojis not allowed on bio? 
​Thanks!