From my experience walking most of California last year I wouldn’t say that “you will have no trouble hitching”. Sometimes it will be easier than other times. Being French won’t effect your ability to get a ride but if you are a male hiking alone without any females that can be a factor. You will go through areas where people will instantly recognize you as a PCT hiker and will be happy to pick you up. You will also go through spots where most of the traffic is clueless tourists who know nothing of the PCT and all they see is a dirty, ragged looking guy who came out of the wilderness. I hiked late in the season, way behind everybody else, so maybe that is another factor.
One spot that sticks out in my mind is Sonora pass. I stood there sticking my thumb out in both directions for several hours. There was tons of traffic but people avoided even looking at me. If I had known there was a trailhead parking lot just over the hill I would have gone there and tried to engage some other hikers in conversation in order to get a ride. Finally I ran into a backpacker and former AT thru hiker who offered to give me a ride and then better yet gave me some of the extra hiking food he had in his car, which was the only reason I wanted to get to town in the first place - to get a bit of extra food to get me through the next section.
Talking to other hikers and backpackers in parking lots is a really good way to get rides and is often much easier than sticking your thumb out or holding a sign. If you feel uncomfortable about going up and asking directly if you can get a ride from someone you can try acting a bit clueless at first and ask for directions. Like, “Excuse me, if I walk down this road which highway will it take me out to?” etc. That leads into explaining that you are trying to get to town for resupply. If you are talking to a person who is any sort of outdoor enthusiast and they find out you are a PCT hiker, you pretty much have a ride at that point.
As far as the law goes, in California at least, as long as you aren’t trying to hitch on the freeway you should be fine. I know of one hiker who even got a ride from a police officer and there was no problems.
aaron111