I have been signing castles, for sieges as long as i can remember.
But the question should be , why do we need to ?
Because if you forget to sign, you cant cast any castle and you loose xp when you die.
isn't it better and more fun to keep the element of surprise and not announce which castle you attack.
Registration should be only for defending clans.
Many time siege starts and ally or friends have forgotten to sign castles. And they just go on grinding, while they could have more fun doing sieges.
It could be something spontaneous, and decided to siege just before or during siege.
Ive seen just a couple of clans attacking castles, while it used to be so many more .
The bigger the sieges the more fun for people.
At the end we all grind to better ourselfs and level up.
Pvp and sieges are a big part of the game.