To solve this I had made a stamp with my name and signature. I had visited a shop that sells stamps, put my signature on a paper and after some days they presented me a wooden stamp with a perfect copy of my signature on it. So when the papers needed signing I gave it to my assistant and she just stamped my sign to all the needed papers!
Of course that means that she could also sign other things as myself but I trusted her and was careful to sometimes glimpse at the papers that were signed (they all had the same template).
I have to confess though that it was really crazy how easy it was to copy my signature and have a way to sign every kind of paper. I presume that if some signature of me was in a non proper place I could complain and a specialist would recognise it...