If you could learn what ward skin your enemy is using, could you know who just warded from over the wall and thus know the position of the jungler without really seeing him?
Or is there a protection in game so that you can't know who exactly warded?
Here is a situation where this could be useful:
You see a ward that has just been placed in your bottom river bush. If it's the jungler, you can know that your jungler can invade top side and not meet their jungler there. If it's midlane that walked down and warded, you wouldn't be able to guess the above.
Best Answer
To some degree, yes they could be used as an advantage if you were able to memorize which ward skin each enemy is using, or vice versa. If you knew their jungler was using the dragon slayer ward skin, and no one else was, if you see that ward being placed, you will know that it is their jungler placing that ward.
It is somewhat hard to acquire this information though, as you would have to see them place down a ward in vision to see which ward skin they have first, and if you aren't roaming or looking around the map a lot, you might not ever figure out who is using a certain ward skin, or it may be very late into the game when you do figure out all the ward skins, and it may not matter much.
Also, being able to remember which person used each ward skin may be hard to do in the moment with everything else that is going on in the game, especially if it is a high pressure situation.
TLDR: Yes, ward skins can potentially give you a slight (dis)advantage.