it is different than the 'normal' sketch icon.
It means you have made an extrude/extrude cut from a sketch having multiple closed groups.
for instance, two squares overlapping, so you have 5 contours in your sketch:
Occasional sketch icon
Not only does your sketch have multiple closed groups (like Tim mentioned), but when you created the cut extrude, only one of those closed groups was selected to generate the geometry. If you have a sketch with multiple closed groups but do not select only one possibility, the sketch icon is still the "normal" one.
If you have questions about an icon this is a good site.
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