Symbol question

Hi everybody!

Could anyone clarify to me… what are those perpendicular lines in the middle of any Symbol in ToonBoom?..
And how do I move them?.. Or make it so that they are in the same place for the whole duration (or exposure…) of the symbol…

Here, I took a screenshot just to clarify what lines I am talking about:


You probably have selected a drawing in the symbol. It shows the center of the drawing.