Brush
Application
Brush is used as a way to draw freely or annotate on the chart. The paint brush is not bound to a specific shape like most other drawing tools.
Style
In Style property dialog it is possible to change the appearance of a drawing line:
Line
Sets the color and thickness of a drawing line.
Background
Toggles the background visibility, color and opacity level for a painting.
Visibility
In visibility properties dialog you can switch a Brush drawing displaying on charts of different timeframes: