Thank you all so much for replying. Indeed it seems that this stamp is used in more blades.
Especially the Aceh sword from Willem was most interesting, because it seems that this stamp was used more around this region. We now have Willem's sword, the one from the Leiden museum and mine with the same stamp and from the same region...
Fernando thank you very much for your links. I see it was discussed before, but I couldn't find it myself, so I think Jim can stop searching where he has seen it before and have a good well earned nightrest...
Thanks again,
Maurice