These chaco liners are some of my favourite ways to mark fabric. Held like a pen, they roll along fabric leaving a fine line of chalk for you to follow for a stitching line or for placement of fabric, for example a pocket on a bag, or hardware. They can be used both freehand and with a ruler.
These are available in blue, silver and white, and the product image shows how they show up on both dark and light coloured fabrics.
Depending on the colour you choose, the chalk can be brushed off, or removed with a mixture of water and vinegar on a 5:2 ratio, dabbed with a sponge – be sure to test on a scrap of your project fabric before using on the final piece to ensure it can be removed successfully. Do not use on non-washable fabric.