I had the same problem. Following the Vadis instructions/pics and the Volvospeed instructions/pics I was unable to find the mark on the crank pullery/gear. I am convinced there was not one to be found.

Then I checked in with my Haynes manual again and saw that the picture in that book showed the mark not 'in a valley in the crank pulley t-belt gear' but rather on the 'hub' that the s-belt crank pulley is mounted on. Since the s-belt crank pulley is shaped like a bowl (and mounts at the 'front' and curves 'back' towards the engine around the hub it's mounted to) it almost entirely covers this part of the 'hub' and thus almost entirely covers the mark.

When I looked for a mark in this location I did find it, but it was damn hard to see. I had to get the light in just the right spot so it would throw the light way down there and get in behind the crank pulled as I described, but yet still be able to see past the trouble-light housing.... it took some finangling. I had to position my head with my forehead on top of the t-belt cover above the cams and my eyes as close to the t-belt cover as possible without letting the t-belt cover obscure my view of the crank pulley. Luckily I had a friend with me who turned the engine for me. It would have been a pretty arduous process if I would have had to turn the engine as well as all that wrestling/repositioning.

If I ever think to do it I will maybe scan that picture and post it up here so you can better see what I mean.

PS - it would be a cinch to see it if the crank pulley was removed, which I suspect is part of the official volvo procedure.
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1998 V70 AWD Turbo 195k+