Not that the sipings have any effect on performace (I did read an article somewhere in which the representative from Continental said that customers expect them so thats why they are on there), but it is nice to know you've installed them in the correct orientation.
I was in a rush installing my first tyre as I had a split in the carcass of my Giant P-R3 tyre and in artificial light I couldn't find any markings or rotation travel at all so I made a judgement call and, as it turns out, put them on the wrong way.
When it came to installing the other tyre the sun was shining brightly and I could just make it out (and I mean very just) so I thought I'd share it with the world and post a picture up. It may seem unclear in the picture - it is worse than this in real life! I've put some post-processing on the image to bring the markings up better. You can't actually make out the point of the arrow but the end of the shaft is just about visible. If you look very hard you can just determine the shoulders of the arrows as well.