Looking for symbol: Shield

You could, of course, use TikZ for this:

The symbol will scale with your font size, since it uses ex to define the path.

\documentclass{article}
\usepackage{tikz}
\begin{document}
\newcommand\shield{%
    \tikz [baseline] \draw (0,1.75ex) -- (0,0.75ex) arc [radius=0.75ex, start angle=-180, end angle=0] -- (1.5ex,1.75ex) -- cycle;%
}

A shield: \shield
\end{document} 

---

If you're feeling fancy, you could parametrise it a bit:

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\begin{document}
\newcommand\shield[1][]{%
\tikzset{
    shield width/.store in=\shieldwidth,
    shield width=1.5ex,
    shield height/.store in=\shieldheight,
    shield height=1.75ex
}%
\tikz [baseline,#1] \draw (0,\shieldheight) -- (0,\shieldwidth/2) arc [radius=\shieldwidth/2, start angle=-180, end angle=0] -- (\shieldwidth,\shieldheight) -- cycle;%
}

A shield: \shield

A wide shield: \shield[shield width=2ex]

A tall shield: \shield[shield height=3ex]
\end{document} 

There is another way to do that: in the milstd package there is a symbol (in fact a rotated logical AND gate), which in fact has a completely different signification, but looks like what you need: \ANDd:

I need a shield symbol and Jake's answer inspired me. I share my tikz code for my shield here:

\documentclass[11pt]{article} 
\usepackage{tikz,pifont}

\newcommand\shield{
\tikz [baseline] \draw (3ex,2.5ex) -- (1.5ex,3ex) -- (0ex,2.5ex)  to [out=-90, in=165] (1.5ex,0ex) to [out=15, in=-90] cycle (1.5ex,1.5ex) node {\ding{51}};}

\begin{document}

\shield

\end{document}