You should edit the voltmeter definition from the CircuiTikZ code. I did it for you by commenting some lines and adding a new line to rotate the label. Actually I created a new component named myvoltmeter, based on the original. I mirrored the inductor too. Please, use siunitx as explained in the package manual.
\documentclass{article}
\usepackage{siunitx}
\usepackage{circuitikz}
\makeatletter
\def\pgf@circ@myvoltmeter@path#1{\pgf@circ@bipole@path{myvoltmeter}{#1}}
\tikzset{myvoltmeter/.style = {\circuitikzbasekey, /tikz/to
path=\pgf@circ@myvoltmeter@path}}
\pgfcircdeclarebipole{}{\ctikzvalof{bipoles/voltmeter/height}}{myvoltmeter}
{\ctikzvalof{bipoles/voltmeter/height}}{\ctikzvalof{bipoles/voltmeter/width}}
{
\def\pgf@circ@temp{right}
\ifx\tikz@res@label@pos\pgf@circ@temp
\pgf@circ@res@step=-1.2\pgf@circ@res@up
\else
\def\pgf@circ@temp{below}
\ifx\tikz@res@label@pos\pgf@circ@temp
\pgf@circ@res@step=-1.2\pgf@circ@res@up
\else
\pgf@circ@res@step=1.2\pgf@circ@res@up
\fi
\fi
\pgfpathmoveto{\pgfpoint{\pgf@circ@res@left}{\pgf@circ@res@zero}}
\pgfpointorigin \pgf@circ@res@other = \pgf@x
\advance \pgf@circ@res@other by -\pgf@circ@res@up
\pgfpathlineto{\pgfpoint{\pgf@circ@res@other}{\pgf@circ@res@zero}}
\pgfusepath{draw}
\pgfsetlinewidth{\pgfkeysvalueof{/tikz/circuitikz/bipoles/thickness}
\pgfstartlinewidth}
\pgfscope
\pgfpathcircle{\pgfpointorigin}{\pgf@circ@res@up}
\pgfusepath{draw}
\endpgfscope
\pgfsetlinewidth{\pgfstartlinewidth}
\pgftransformrotate{90} % rotate the label
%\pgfpathmoveto{\pgfpoint{-\pgf@circ@res@other}{.8\pgf@circ@res@up}}
%\pgfpathlineto{\pgfpoint{\pgf@circ@res@other}{.8\pgf@circ@res@down}}
%\pgfusepath{draw}
\pgfnode{circle}{center}{\textbf{V}}{}{}
\pgfscope
% \pgftransformshift{\pgfpoint{-\pgf@circ@res@other}{.8\pgf@circ@res@up}}
% \pgftransformrotate{45}
% \pgfnode{currarrow}{center}{}{}{\pgfusepath{stroke}}
\endpgfscope
\pgfpathmoveto{\pgfpoint{-\pgf@circ@res@other}{\pgf@circ@res@zero}}
\pgfpathlineto{\pgfpoint{\pgf@circ@res@right}{\pgf@circ@res@zero}}
\pgfusepath{draw}
\pgfusepath{stroke}
}
\makeatother
\begin{document}
\begin{circuitikz}[american, scale = 2]
\draw
(0,0) to [sV = $V_m\cos(\omega t + \theta)$] (0,2)
to [C = \SI{10}{\pico F}] (2,2)
to [R = \SI{250}{\ohm}, *-*] (2,0)
(0,0) to [L = \SI{300}{\micro H}] (2,0)
(2,2) -- (4,2)
to [myvoltmeter] (4,0)
-- (2,0)
(0,2) to [short, *-o] (0,3)
(2,2) to [short, -o] (2,3)
(0,3) [yshift=5pt] to [open, v=$v(t)$] (2,3)
;
\end{circuitikz}
\end{document}

circuitikz
env. say\node at (1,3) {$+\; V\; -$};
. Also without an arrow measurement units are simply circles hence easy to place it using standard TikZ commands.