Have you qualified the spots as theirs? I would make sure that they know IF you work on it there is some risk of brightening the areas.
I'd try a good protein spotter than has an enzyme in it and see how it fares from there. Unfortunately if that doesn't remove it then I think you may need some type of a peroxide type spotter.
I'd use a q-tip or towel and rise with upholstery tool. Allow to dry and evaluate the results. Don't try to do too much. Several attempts are better than one aggressive attempt.
I agree.
My father worked in the dry cleaning business for 25-years before starting this business. They have the solutions, the spotting board and air pressure to make easy work of it.
i would start with q tips and some spotting agents you think might work, watch you dont get too close to the signatures, and do not over saturate, hence the Q tips.