That's right, there's no locking system.Hi Hermann,
I have read somewhere that the Gitzo GT1545T does not have any real locking system/screw to prevent the head from turning/unscrewing from the tripod.
Not really. I make sure I screw the head on tight, that's it.Do you notice any loosening of the head from the tripod, when carrying it around with the scope on it?
Well, I always habitually check if everything is OK when I carry the scope on my tripod. Becomes sort of second nature. Never had any "accidents" in well over 40 years of birding.(I would probably be walking, cycling etc with the scope on the tripod and woukdn't want to have to worry about that or to have to check it when on the go.)