I also saw that for sale and did some research of 
my own on it. While I can confirm that marking 
does appear on legitamate Fruits Basket layouts, 
I also confirmed that it appears on the layouts 
of at least one other completely different 
series. It's possible that it is a studio marking 
of some kind.

It does not say anything close to the Fruits 
Basket title, if that was what you were wondering.

Besides not being able to find that sketch's 
image in the anime, the style of the drawing is 
completely inconsistant with all Fruits Basket 
layouts I have seen. . . even rough ones.

Many Sharp Smiles,
--Drac