watchword
noun [ C usually singular ] uk/ˈwɒtʃ.wɜːd/ us/ˈwɑːtʃ.wɝːd/
口号;标语;格言
(a word or phrase that represents) the main ideas or principles directing the way that someone behaves or the way that something is done
And remember, let caution be your watchword. 切记，把谨慎当作你的格言。