Hi Pilou - meshes do not have a single "seam edge" like a closed NURBS surface does.

A NURBS surface is like one larger sheet of paper, and a closed surface like a cylinder has a "seam edge" when the sheet of paper is rolled up like a tube and the opposite edges touch each other.

Polygons on the other hand are like a lot of little fragments, they are not like a big bendable sheet of paper and so they do not have a special seam edge, they only have a bunch of polygon edges.

So that's why there is no seam edge display option in that location, because when you are looking at a mesh there are no seam edges there.

Does that make sense?

- Michael