Motto

A motto is a phrase meant to formally summarize the general motivation or intention of a social group or organization. A motto may be in any language, but Latin is the most used in the Western world. The local language is usual in the mottoes of governments. In informal ways, it can be a rule or slogan someone follows, or lives their life by. (Source: WikiPedia)

Merriam-Webster Online Dictionary

motto(noun)

1. a sentence, phrase, or word inscribed on something as appropriate to or indicative of its character or use

2. a short expression of a guiding principle