Thread Tacking
This is a technique used in professional and high-end sewing. It's essentially temporary stitches, like basting. They are quick stitches that don't need to be perfect.
Couturiers and suit tailors often use tailor's tacks to mark a fabric to prevent leaving any permanent markings, especially if you're using costly, luxurious textiles. Tacking is best used for delicate, thick, or textured fabrics.
Thread tacking is a great way to utilize old threads that are too brittle for your sewing machine as they can snap immediately through threading. Be sure to use a contrasting color thread for better visibility.