I often mark before loading, but it depends on if I have a plan ahead of time or not- if using stencils & chalk *pounce* I mark as I go. it depends on what I am using to mark...chalk brushes off- so I use it as I go- if using my ceramic pencils I mark ahead of time when I can lay it out on the table (hard surface) & draw nice thin light lines....just depends on what you use & what is easiest for you- if pin basting I think dealing with the pins in the way would (could) be an issue- but if thread basting, or spray- then marking after might be ok- ...do what you want...everyone has their own methods.