Every untouched factory car I have had through my shop had the part # at the cross member sockets. But as 72blu states.... it don't really matter, turn it 180* and it still twists the same!
Although I pretty much only run aftermarket bars in all of my cars I like to put any markings to the rear so you can read them in the anchors. It’s a nice check to have when you’ve had everything apart and back together a few times. So at the end of a long day (or days) you can look and see that you haven’t accidentally screwed something up and swapped the bars side to side.