Is there a designated symbol for the negative sign in, say, -16?

I am not a fan of typing numbers in the text in mathmode. It's fine if you use a complete font, but what if you decide to change the math font later? I prefer to use the textminus from the textcomp package. If your editor is unicode capable you can enter the proper minus symbol directly.

Edit: siunitx is able to handle numbers correctly as well.

Edit 2: To respond a bit more to the question asked, there is no typographical difference between a 'minus' and 'negative' sign. The difference is the kerning: With $-12$ the sign is close to the number, with $10-12$ the minus has appropriate kerning between the numbers. In short, there should be no need to resize the minus sign for negative numbers as a good font should have a minus sign so that its length blends in well with text.

\documentclass{scrartcl}

\usepackage{textcomp}
\usepackage{mathpazo}
\usepackage{eulervm}
\usepackage[utf8]{inputenc}

\DeclareUnicodeCharacter{2212}{\textminus}% requires a unicode capable editor

\usepackage{siunitx}
\sisetup{
   detect-mode,
   detect-family,
   detect-inline-family=math,
}

\begin{document}

\noindent
Number \textminus10 (textcomp minus)\\
Number −10 (unicode minus)\\% requires a unicode capable editor
Number -10 (normal text minus)\\
Number $-10$ (all math mode)\\    
\vspace{1ex}
\noindent
Number \num{-16} (siunitx textmode. No bug, my bad. Sorry Joseph)\\
Number $\num{-16}$ (siunitx mathmode)

\end{document}

David's

Using a hyphen as in (3) is just horrible, it's all wrong.

got me thinking and I guess a nice alternative (if you don't like the default length) is to define the command \minus like that:

\documentclass{article}
\usepackage{graphicx}
\newcommand{\minus}{\scalebox{0.75}[1.0]{$-$}}

\begin{document}
  $\minus 16$

  $-16$
\end{document}

where 0.75 is the horizontal scaling of the box.

\documentclass{article}

\begin{document}

1: ${}-16$

2: $-16$

3: -$16$

4: $^{-}16$

5: $^{-}\!16$

\end{document}

I think the normal usage is as in (2) with the normal length minus sign, If used in prefix position TeX does give it closer spacing than when it is used as a binary operator (compare with (1) ).

Using a hyphen as in (3) is just horrible, it's all wrong.

It may depend on national customs but here in the UK for educational use it's customary to distinguish the number -16 from 0 - 16 more clearly so that you can wrote 3 - -16 etc and distinguish the prefix version as part of the number from the infix operator. Using one of (4) or (5) according to taste might be suitable for that usage.