Marking fabric is always a bit of a hangup for me. I tend to make projects over several weeks so selecting a marking method that will last for a long time, be easily removable, and not leave anything behind is important to me.
I love couture sewing and tailoring. Both of these “schools of sewing” use thread as a the primary marking method. I adapted a method that involves first using a tested fabric marking pen or chalk and then going back over with thread.
For pattern markings that show up as dots, triangles, squares, etc. I tend to use the tailor’s tack. The tailor’s tack can be done with any kind of thread – although fine silk thread leaves no trace, even when ironed. The tacks are easily removed and stay put through ironing and fittings.
To make a tailor’s tack, place a small stitch in your marking point. Pull through leaving a tail and go back around on the stitch you just made. Cut leaving a tail and soldier on!