The trick marker is a fantastic water erasable pen by Prym.
 
Use it to draw stitch lines and outlines on both woven and knit fabrics and if you go wrong, don't worry it's water erasable.
 
To remove any marks rinse the fabric in cold water or dab with a damp cloth and watch as they vanish before your eyes! All marks should be removed before ironing or dry cleaning as heat can set the lines permanently.
 
This pen comes in two colours and two different nib sizes (standard and extra fine)
white - suitable for darker coloured fabrics 
blue  - suitable for light coloured fabrics. 
 
Please store vertically with the cap downwards to prevent it from drying out.
 
Warning: Before use test the pen on a discreet part of the garment e.g. a seam and if the marks disappear with water it's safe to use!