signatory
noun [ C ] uk/ˈsɪɡ.nə.tər.i/ us/ˈsɪɡ.nə.tɔːr.i/
签约者;缔约国
a person, organization, or country that has signed an agreement
Most western European nations are signatories to/of the North Atlantic Treaty Organization. 大部分西欧国家都是北大西洋公约组织的缔约国。