Help need to explain odd mark around a maker's mark.

I have a collection of Luneville Old Strasbourg earthenware. As I was taking the picture of the Maker's mark I noticed a very faint irregular line around the mark. It is only visible when the light shines just right so I am unable to get a picture. It looks like the mark was put on a pieces of transparent paper and applied under the glaze. I have hundreds of pieces and I only see it on a set of 10 pierced edge dinner plates not the dessert plates. It is just very odd. I can see it plain as day when I tilt the plate but very hard to get a picture. I took a picture with my digital microscope and you can see the faint outline. I am going to sell these and want to be sure they are not faked makers mark.

 

Just curious, this plate looks very typical to me, is there a lot of faking going on with Luneville and are the fakes of high quality like this?

I didn't know plates like this were faked - are they very valuable?

 

I would guess the square outline marks the edges of a decal.

 

That was my concern since I am sure in 1880-1920 they would not have used a decal. All of the shapes are irregular however and none identical. I did not find any reference to fakes on the internet and the quality is just like the others with out the outline. I am baffled but will put them up for sale . I handled these a lot checking for blemishes and did not notice the marks until the light hit them just right.

 

Luneville plates like these are going for $30-40 dollars a piece.