If you are interested in this kind of stuff here's a dump of the texture m24_02_o0472_01_a for it with the snake-head in bottom right.
And the model is m24_02_00_00_002505 if you wish to check it out yourself.

The snake-head archway might have been one of the first signs that you are now on the path towards Land of the Dragon.

Importantly the path towards it would have been accessed from the Grand Cathedral.

While no literal dragons were depicted for the area, if we subscribe to the Land of the Dragon hypothesis it wouldn't be a far-fetch to make a connection between snakes and dragons in a FromSoftware game.

There's an old prototype model of a castle in the mountains directly behind Grand Cathedral that Sophie at Sinclair Lore speculates could be related to the concept art for "The Land of the Dragon"

More about it here:
www.bloodborne-wiki.com/2021/04/the-...