The Tour Saint-Jacques, just north over the river from Notre-Dame, is the traditional gathering point for pilgrims starting in the northern parts of Paris, or travelling through Paris on their own longer Ways.
Then it depends whether you're going via Orléans or Chartres.
South from there on the Way to Orléans you take the Rue Saint-Jacques from Notre-Dame towards the Rue du Faubourg Saint-Jacques and so on.
The Way via Chartres can be a little more DIY for getting out of Paris, but it becomes more definite from Rambouillet. One option for the Chartres variant is to follow the Orléans route as far as Saint-Rémy lès Chevreuse, and then make your Way from there to Rambouillet, but there are ways to get there with less suburbia and more nature.
On my 1994 I actually left from close to the Place de la Bastille, towards the Tour Saint-Jacques, as I had lived near there at a friend's place over the 10-day/2 week period before starting. The first 20K from central Paris was on my old hike training route to Jouy-en-Josas, about half way to Saint-Rémy.
There may be no yellow arrows until you're well away from Paris, possibly not until you're rather close to Spain. In France, you mostly follow the FFR hiking route waymarkers (Fédération Française de Randonnée).