There is a known issue with these extensions!
One of the possible marks is the alignment mark, a circle with a cross that is meant to guarantee that the color channels are properly aligned when printed.
Ok, I understand. Is there a way (double circle, or another convention?) to design an alignment mark which doesn't need to be printed in pure black ?
And then, I agree that this functionality shoul move to the export dialog.
I have worked on the extension so that it looks like Scribus' s PDF dialog. Bleed marks, crop marks, and registration marks are available, with some options (offset, bleed size). I plan to update my files in launchpad, so that you can see what it looks like. If you give me a clue, I can change the current alignment mark so that it doesn't require pure black. Then, tell me if you think it's a good thing to keep it as a temporary extension, since the funtionality doesn't exists as a PDF export dialog. I don't remember having seen it in the blueprints. We sure should add it.
Thanks for your comments. -- Nicolas