Floating icon shape circle appears on the display when the S pen gets detached in Note5?

The Floating icon in Samsung Galaxy Note 5 is to activate Air command quickly. Just simply tap on the floating icon to open Air Command from any screen.  

You can easily access S Pen functions from any screen and move the floating icon and place it wherever you want. When the Air command panel is closed, the Air command icon will remain on the screen. To remove the icon, tap and hold floating icon, then drag it to Remove at the top of the screen.