The Helvetica Neue font is very similar to the original Helvetica font in design. This font also has a very neutral design and can be used in all kinds of signage. It can also be used in legal and official documents.
However, the Helvetica Neue Bold is a darker version of the Helvetica Neue and is used mainly to highlight or emphasize some points in a document. The bolder version of the Helvetica Neue is especially suitable for signage because it can be easily read from a distance and also because it stands out among other fonts because of its simplicity.
See also: Free Helvetica Font: Helvetica Neue