White transfer paper - The easiest way to mark sashiko designs onto dark indigo cloth is to use a wax less smudge proof white transfer paper. Loew Cornell is my favorite and transfers a very clean white line that holds up throughout small projects. It comes in two sizes: 9"x 13" and 18" x 36" sheets.
Stylus or ball point pen - My favorite marking tool is the Sewline 3 in 1 pen; it has a great rounded tip metal stylus, perfect for transferring a bold clean line. It also has a fine line white chalk pencil, very useful for going over any tracings that need to highlighted.
Clear or masking tape
Be sure to test your transfer paper first to make you are using enough pressure to produce a clear clean line. Mark carefully as not all transfer paper markings will wash out. Loew Cornell white transfer paper however, will gradually fade as you work your project and can be removed with a damp cloth and by pressing from the wrong side with an iron on cotton setting.
On a very firm surface, place the pattern on the cloth and tape in place on one side.
Slip a piece of transfer paper in between. Be sure to place the white side of the transfer paper down on your fabric.
Test your line to see if it is transferring well. The taped hinge on one side allows you to check your line without disturbing the placement.
Tape all four corners outside the design and use either a stylus or a fine lead pencil or ball point pen to trace and transfer the design.
If a sashiko design has a simple shape or curve, the shape can be traced onto and cut out of template plastic or card stock and used to trace around onto the dark fabric with a chalk pencil. Geometric designs with straight lines can be transferred using rulers and transfer paper or by marking a grid onto the fabric with a chalk pencil.