I would suggest that even with the best in pencil or chalk technology I would wash the material before stuffing, you need to take into consideration the OCDness of the peron for whom the uq is being made.
Prepair not the path for the hiker but the hiker for the path.
All fabrics are shipped with sizing, stablizers and other chemicals (including formaldehyde in many cases.) These need to washed out before use. This has little to do with pencil marks but as that was the original question that is where I spent my reply time.
I may be slow... But I sure am gimpy.
"Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
Mrs. Loftus to Huck Finn
We Don't Sew... We Make Gear! video series
Important thread injector guidelines especially for Newbies
Bobbin Tension - A Personal Viewpoint
That looks like the same kind of pen to me.
Fibre tip and dissapearing ink.
My last one was a purple colour with white top, I can't help any more than that as I've just looked for it and found the pen fairies have abducted it.
It does have 'Air erasable' written on the side though and it came from a sewing shop.
Its no good for dark colours though as pointed out above