When I copy a DVD is there any trace or maker left on the original DVD to show that it has been copied?
It can depend on the software that you are using to back up the original DVD. I know that some trial versions of some copy programs do carry a watermark logo until you purchase the registered version.
I believe this question was asked before and James said no. It might take awhile to find that thread though.
I believe the fact that you're using blank media shows the disc has been copied by virtue of having a backup. However, as far as the original disc, goes, no. You can't write to pressed media.