Those blue and purple pens come in two types; one that disappears on it's own and the other with water. The second one you have to be careful and not get hot either by an iron or the sun, etc. You also need to surmerge it in water and let it soak or they'll come back. I can understand the Frixon Pen issue; I like them but would probably feel the same way. When I was marking a quilt I used a sliver of soap which works great unless it's on a light colored fabric. The other thing you can do is use the blue painters tape. It removes easily but will stay until you're ready for it to come off.