Nice, you're improving!!
I'm not a fan of cut-off siggies like the top part but I don't think a border will look right for this siggy either.
Instead, you could try erasing that part of the brush so the sig won't be cut off. I did a quick and rough example because it was too hard to explain the part I'm talking about in words @_@
Or if you want that curved line in, you could take that pink colour, use a pen tool and draw in your own curved line (you can tick the Simulate Pressure box when you do Stroke Path after drawing the line with pen tool, so that the line doesn't end bluntly and kinda narrows at the end).
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