Will be ready to go into town tomorrow to purchase what marker(s) I need to mark on my grandaughters Sunbonnet Sue. I am quilting a diagonal/cross-hatch behind the Sue's.
I want the marks to come off completely- What do you recommend ?

Also I am making a label on the back to identify different fabrics from family members and I will also need a permanent marker and was wanting something that doesn't run but will stay forever. What do you recommend for this totally different part.

i use a bohin pen its white chalk, and i have used a purple felt type pen that disapears completly but I would suggest doing a test run on any product you choose

You could use painter's tape for the crosshatching - then there are no marks!!

Use a Pigma pen for making the label. There are several different colors available & it is permanent.

for the most part, i use a wash out blue marker. white with blue cap. Dritz maybe. still, test on all fabrics.
Micron pigma pen .05 in size to write label. heat set few seconds with iron too. i always do. works well. i was in swaps for years and no problems.
also i use a Hera plastic marker for lines like cross hatching. it makes an indention in fabric, nothing to wash out.

I use dritz blue water soluble pens. The only time I had a problem is when I let a quilt set for over a year before finishing. I think they are perm. after 2 months or so, but I've had good success for up to 6 months.

I buy the purple disappearing ink pens. Fades off or just spritz. Some have a finer point for marking now.

I have started experimenting with the Pilot Frixion ball erasable gel pen (phew ... that's all on the package!) Anyway, not only is it erasable ... it is thermo-sensitive. Passing a warm iron over it also makes it go away. So far I have only used it on the back side or the fabric and it DOES go away with the heat of the iron. The package I have comes with ried, blue and black pens. As an aside, I also do like the fine line it makes.

I used the Frixion pen as well and I reallly liked it and the marks came out completely.

I use chalk board chalk sharpened with a big pencil sharpener. It comes in colors if you need them. Have never had a problem with it coming out.