Unknown symbol in layer panel

[Jogi]

Hi there,

recently there is a strange symbol in the layer panel and I don't know what it means.
My problem is: When I add a new layer and fill it with a pattern, the pattern does not show
in the layer icon - it still shows the transparancy pattern. When I set this layer to overlay, the
strange symbol occurs. I'll try to attach a picture of the symbol, hope it works.

I appreciate any hints and suggestions.
Thanx in advance.
Jogi