Hate answering a question with a question Red but would Chinese drivers actually know what we consider to be the universal sign for a hitchhiker? Thumb out with a wave? Or would they just think it was a foreigner giving them the 'OK' sign because their driving is so good?

I've done this before, twice!  The first time I was with another foreigner and a Chinese colleague (girl).  We had went to a local botanical gardens type place after dinner...a bit out in the sticks.  It was easy enough to find a taxi to go out there, but after it got dark and it was time to come back....no such luck.  Me and the other foreigner were ready to just hoof it back, it was only 2 or 3km....not too bad.  The girl wasn't having it.  She waved down one of those small mini utility type vans....you know, the Chang An type with the Star Trek logo.  We were a bit apprehensive to just jump in, especially as we hadn't been in China all that long.  Ended up getting back ok, and paid the dude 10 rmb for his trouble.

The second time, I was waiting at the bus stop with a couple of Chinese colleagues, waiting for the slowest bus ever to arrive to take us into town.  Some random dude stops and asks us for directions to some place into town.  Again, it's another Star Trek van, lol.  He ends up giving us a ride into town, just so we can show him where to go.  He was delivering boxes of wine....which served as our seats, no time to whine about seat belts. 

Both times I had Chinese with me, and this is in a 4th tier city.  Not sure I would try it alone, or in a bigger city.

I doubt it's possible here. It's pretty easy getting a ride by some average Wang in a small sedan but then it is a pirate taxi. 

Happened once, it was in the middle of nowhere in Xinjiang. My wife and me trekked around in a mostly empty Swiss-like valley (complete with glaciers, pine forests, etc) lost in the middle of the desert, next to Hami. We were waiting for a bus. 3 dudes in a car stopped and proposed to give us a lift to Hami, for a very reasonable fee. This kind of things seemed common in this area (mostly vast expense of desert). The ride was nice, one of the guy had plenty of interesting stories

As above, with the random car stopping, flinging open the door and gesturing to get in.  No money asked for, or paid.  Just a friendly "thanks a lot mate!" uttered in my very best Chinese...like this, "shay shay knee!"

This has happened to me 4 or 5 times in and around my small city in Xinjiang.  On two of those occasions they slipped some John Denver into me while we drove along.

But this isn't actually hitchhiking, I know.  So...no, I haven't.

Chinese always put 'hitchacking' thumb up, after you bottom-up baiju, so I'm guessing driver might stop his car, and come out with the bottle in his hands. 

Thumb-up also means 'awesome' in Chinese.

When I need ride, my choice are always bicycles. I should say 'girls on the bicycles', however none ever stopped, and offered me a ride yet.