A scratched item such as an indoor tree, a piece of furniture or a scratching post becomes a personal territorial marker of the cat, because the scratched appearance is readily visible to other cats who might be in the vicinity. (birdneckanimalhospital.com)
Three principles should be kept in mind: 1) Once a cat starts scratching an object she tends to return to it; 2) prominent objects - which make the best territorial markers - are favored, and 3) the texture of a potential scratching area influences whether it is used or not. (birdneckanimalhospital.com)