What is Nota Bene?

Legal Definition
Nota bene (/ˈntə ˈbɛn/, /ˈntə ˈbɛni/ or /ˈntə ˈbni/; plural form notate bene) is a Latin phrase meaning "note well". The phrase first appeared in English writing circa 1711.

Often abbreviated as "N.B.", "N.b." or "n.b." (US English); "NB", "Nb" or "nb" (UK English) nota bene comes from the Latin roots notāre ("to note") and bene ("well"). It is in the singular imperative mood, instructing one individual to note well the matter at hand. In present-day English, it is used, particularly in legal papers, to draw the attention of the reader to a certain (side) aspect or detail of the subject on hand, translating it as "pay attention" or "take notice". While "N.B." is often used in academic writing, "note" is a common substitute.

The markings used to draw readers' attention in the medieval manuscripts are also called nota bene marks. The common medieval markings do not, however, include the abbreviation N.B.. The usual medieval equivalents are anagrams from the four letters in the word nota, the abbreviation D.M. from Dignum memoria (Worth remembering) or a symbol of a little hand (☞), called a manicule, with the index finger pointing towards the beginning of the significant passage.
-- Wikipedia