The minus in front of a sketch tells you that the sketch isn't fully dimensioned. Inside of the sketch you will see that there are blue elements. Everything that is fully constraint becomes black.
In this case the position of the point isn't fully determined. It seems to be a 2D sketch, so then you would need two dimensions or a combination of dimensions and relations.
Since you are using a newer version of SolidWorks I can't open your files.
You shouldn't just want to get rid of your minus sign, you want to properly define your sketch, in this case the positions of all points. You can create a horizontal center line from the midpoint of a vertical edge and use the mirror tool to copy the first point. Then create a vertical line and copy the two points to get four.
You could also select two points and make them horizontal/vertical using the menu that pops up on the left.You'd still have to add a few dimensions though.
If you don't want them mirrored, you should just dimension all points.
It depends on your design intent. If all hole are symmetrical, then add two center lines and add symmetrical relation