Discover renderer line symbol type

I'm trying to figure out how to discover if the symbol class from a simple renderer is CartographicLineSymbol in vb.NET

According to the documentation ISimpleRenderer.Symbol returns ISymbol.

According to the documentation ISymbol implements several line symbol classes (CartographicLineSymbol, HashLineSymbol, etc.)

I set layer's symbol "Type" to "Cartographic Line Symbol" in the properties and yet this code is not working:

Dim rendLinks As ISimpleRenderer = geoLyrLinks.Renderer
Dim aSymbol As ISymbol = rendLinks.Symbol
If TypeOf aSymbol Is ICartographicLineSymbol Then
MessageBox.Show("i'm a cartographiclinesymbol")
Else
MessageBox.Show("NOT a cartographiclinesymbol")
End If

Can someone tell me what I'm doing wrong? Or can someone tell me how to simply retrieve the symbol class from a simple renderer?