I've tried to do some Counter Battery today and it seems that either I'm doing something wrong or there are no artillery tracers in WoT. I've read a few guides and it seems that if my tank is facing in the right direction I should be able to see the tracer of an artillery after it fires. After playing 10 matches I've seen none regardless of spending the whole match looking for tracers in common arty camping spots. How does this work in the 9.12 (current) version?
While I'm not a huge fan of playing arty, I've done a bit of counter battery fire in patch 9.12 and 9.13. While there still are arty tracers (just like there are shell tracers for all tanks) arty tracers are nowhere near as obvious as they used to be. In recent patches, a tracer will be seen as a tiny white steak departing the arty's location very quickly. Tracers are quite hard to spot, and even harder to find the exact point of origin of. So while counter battery fire is still a viable strategy, I wouldn't recommend it unless you are already experienced, especially since long range accuracy is so rng dependent. However, if you really have your heart set on cb fire, listen closely to the sounds- there will be a telltale "whiff" sound when arty fires in the region you're looking at.
I have been playing arty quite a lot and most of my oneshot kills(or kills in general) come from Counter Battery. As said in the comments: snow maps make it a lot harder as the tracers have some white, yellowish color and they are only visible for less than half a second.
Some tanks have a very small gun and the width of the tracer seems therefore smaller making it much harder to spot. Additionaly, some tanks have very low range or a great shell trajectory which often puts them in locations you less expect them. The best example being the FV304(that mini arty). I has a small caliber, low range and can hit almost anything.
If I did spot an arty shooting I often aim behind the tracer's starting position. I do this because it seems the tracer trails starts when the shell leaves the gun and some arty have a very long gun. By aiming at the starting point you might shoot just in front of the arty which will alert him and possibly make him reposition himself.
The second goes for any tank actually, but you shouldn't forget about it: the shell trajectory should pass through the enemy tank to make sure you have a bigger chance to hit it.
Damage doesn't matter, a direct hit is always a kill, even when shooting at an arty 2 or more tiers above you. It's mostly accuracy that is important, so don't try this in an M12...
This mostly comes from personal experience.