There was an attempt to exploit an offensive throught the Saarland region (Saar Offensive). Even if a large scale offensive were to be undertaken, it would have failed, and for several reasons:

1- Despite an overwhelming superiority, French military doctrine at that time did not allow for offensive warfare, and because it was so ingrained there also no flexibility in changing this method in any timely manner, certainly not as on-basis initiative would have required.

2- Allied intellingence at the time was very faulty. The French or the British could not have known to any reliable extent that the might of the German Army was in the east. It's quite easy to criticize the Allies for not taking the offensive given what we now know, but at the time, recieved wisdon told the Allies it was probably not a good idea.

3- Contrary to popular belief, the Seigfreid Line was not unmanned. The bulk of the German army may have been in Poland, but the Seigfreid Line was still manned and the Saarland well sighted in with their artillery pieces, and artillery was one of the biggest concerns of the French commander, a la
WW 1 doctrine again.

4- The topography of the region is not very good for large scale offensives going east. The Saar valley is a nice big bowl with hills and mountains all around. Not exactly an ideal place to thrust entire armies through. this is one reason why the French developed the Dyle plan, because they fully expected the Germans to do what they once did before, go through Holland and Belgium, because these are regions very suitable for mass movements of troops and tanks.

Of course, Holland and Belgium had declared themselves to be neutral, and France wasn't the kind of country to violate her neighbors to the north. Hitler on the other hand, had no problems whatsoever.

I believe the Saar offensive gave many French commanders a somewhat rude awakening as to the many defeciencies within their doctrines, but sadly they failed to capitalize on wide-scale improvements during the following Phoney War. The best thing the French did was put a halt to that little offensive, it was really their only sensible option.