Jeff,
I found this online. It is from the Lot Notes from a Christies Auction of a Patek Phillipe. They state that it is due to being designated for the French market. I know this info is easily found online, but this is the best 'source' I've found to date. Here is the excerpt..

"As a matter of fact it is the only example of this reference in yellow gold known to exist featuring "FAB. SUISSE" in the combined date/moon phases dial, a designation generally reserved for watches supplied to the French market. This fact is underlined by the case back, stamped with French import marks and the "Guillermin" retailer's stamp, in addition to the regular Patek Philippe signature, serial and reference number. "

Link is here: http://www.christies.com/LotFinder/lot_details.aspx?intObjectID=5257830
Click on 'Lot notes' for the full text

Stewart