What are those things at the wing tip of an aerobatic aircraft? See:


The radially placed needle-like things that resemble a snowflake in the first picture.
The triangular structure in the second picture.
In the third picture, the object placed on only one wing
In the last one, it's also placed on one wing but this one is perpendicular.


What are those things?
They are external attitude references. They're aligned with the aircraft's axes and positioned along the pilot's line of sight to give a quick visual guide to the aircraft's attitude during aerobatic maneuvres. 

You can see the alignment more clearly on this photograph