Have a look at the following, just posted by "nickd" on the Horological Meanderings discussion forum, under the subject line, "You owe me a beer" -- http://www.watchprosite.com/show-forumpost/fi-17/pi-4690098/ti-718203/s--8/

This tells us that the Fab. Suisse was required, at least in 1936!!

Laurent: Does this translation look right to you?

Jeff

Did some digging as this has intrigued me as well. Getting there slowly.

doc.rero.ch ,25,18,19360219.pdf

News letter of la Federation Horlogere Suisse, 19 Februrary 1936

My rough translation (parts of it are a pig to translate)

Customs
Label "Fab. Suisse".
Exporters have become attentive to the decisions that have been taken by the Administration of the French customs concerning the placing/fixing of the place-of-origin markings for horlogical products. The markings "fab. suisse" must be palce, whenever space allows, as close as possible to the make itself, to the side or immediately above or below. Only small watches, where a lack of space prevents the placing of the markings in accordance with the above instructions, can have it below the 6 marker. In order to prevent difficulties and the return of packages, exporters would do well to conform to the above mentioned instructions.

It's talking about "fab. suisse" as a correctif, which suggests it's being placed there to correct something - perhaps there were already French laws insisting that things be in French, so it was correcting the "Swiss Made". Perhaps one of our French legal people can help out here. I wonder if it's also to do with the fact that some Swiss manufacturers had factories in France (eg Zenith) and it was to do with Swiss watches being assembled in France and labelled "Fabrique en France". This is pure guesswork, so don't quote me.

I found some other journals of the time period that all have articles or comments about trade agreements/disagreements between Switzerland and France, so it sounds like an on-going saga. I got back as far as 1920 without finding specific references to "Fab. Suisse", but still plenty of stuff on trade agreements. Don't forget that France had its own large clock and watch industry within spitting distance of Switzerland.

I'll dig some more when I have time.

nick

Douanes
Marque « Fab. suisse ».
Les exportateurs sont rendus attentifs aux décisions qui ont été prises par l'Administration des douanes françaises, concernant l'apposition du correctif d'indication d'origine pour les produits horlogers. Le correctif « fab. suisse » doit être apposé, toutes les fois que la place existe, aussi près que possible de la marque elle-même, � côté ou immédiatement au-dessus ou au-dessous. Seules les petites pièces, où un manque de place empêche d'apposer le correctif conformément aux décisions ci-dessus, pourront le porter au-dessous de 6 heures. En vue d'éviter des difficultés et voir des cous refoulés, les exportateurs voudront bien se conformer aux indications ci-dessus.

: I'd wager France was in the top 3 European markets for Heuer, along
: with Germany and the UK. The number of watches we see with the
: "Fab. Suisse" marking is not even close to being
: commensurate with that, even if it was only over a short
: timescale. So totally agree, it seems most France-bound watches
: have unmarked dials; now if we could only figure out why!!