Hello loppp,
"Fashion" refers to styles and customs prevalent at a given time. It could be clothes, accessories or jewelry.
"Fashion statement" means wearing certain clothes or jewelry to convey a message. It expresses something about the attitude, life style or point of view of the wearer regardless of the gender* could be a male or a female*.
For example statement T-shirts would carry an image or name of your favorite sport team. A statement jewelry would carry your initials or that of you and your girl.
And as Jura mentioned women in particular like to state their wealth , gorgeousness ,style etc through wearing certain jewelry.