Old French post cards

A favorite Paris pastime is browsing through the Marché aux timbres on avenue Gabriel.  In my mind, it is one of the best shopping places for authentic bits of France that are almost impossible to find outside of the Hexagon -- at least in terms of selection.  And which you can take home without weighing down the luggage.

For about an hour I took shelter (kind of) from the dripping rain under a number of tents of stamp and postcard merchants.  If my nice leather flat shoes hadn't been soaked, I would have stayed longer.  Yes, some of us must suffer: caught in the Paris downpour!

This postcard, from around 1910, caught my eye:  a manif!  "Place de la Concorde (Manifestation)."  With the Eiffel Tower in the background.

There are so many comments and complaints from expats and tourists about "oh those @#%*& demonstrations in Paris."  And I share the frustrations.  Kind of.  Because, as this points out, really, they are just a part of Paris tradition.  Well before 1910.

As regular as rain.

But I have no idea what the manifestation was about.  Any ideas to help solve the mystery?