Hi Mauro,
I think I remember seeing this sword when it was offered for sale.
I do not have many resources for Mossi swords. I had one takouba that was discussed and we thought it might be Mossi as it was collected in Burkina Faso and had an unusual and very high pommel spike. That sword is here:
http://takouba.org/takouba11/ However the Mossi attribution was merely a guess.
What I do have are some photos of Mossi warriors. I have to admit I know relatively little about Mossi culture, they were a pagan kingdom on the edge of the Islamic states. They were often at war and conducted raids against the Muslim peoples, like the Hausa. They are also well known for bronze working and their statues have similar motifs like your sword.
So I would agree the sword is Mossi for sure and a nice example. What I am not sure is how much overlap or borrowing occurs with Mossi weaponry. The one photo I posted it almost looks like one man has a kaskara (on the right side of the picture) and the horseman has armour on his arms and what looks like the pommel of a Mandingo sword over his shoulder.
A very interesting and understudied culture I think. I found one interesting resource on Google books but it has very little about swords as you will see.
http://books.google.com/books?id=b56...=sword&f=false