Have to give this one to my playing partner this morning - 212Y Par 3, a green that neither of us have ever dropped on, a few low burners that have rolled onto the green. But today he took a 6 iron (he's a very big hitter), hit a perfect draw shot, and landed 6 feet past the hole. It wasn't even the distance he gets with that club, it was the shape of the shot that was so pretty.
Tee markers are not clearly defined as a device, but as previously mentioned, they are defined as immovable (while teeing off) obstructions. I can't think of (or find) any prohibition of taking a stance with a foot on any other immovable obstruction, a sprinkler or a drain grate as examples. If a tee marker would somehow be considered a device, it stands to reason that a sprinkler head or a drain would be too. I tend to agree with @Fourputt. Weird as it might be, I just can't see why it would be prohibited.