Unusual versions of 3 letters

Question

I'm trying to type up notes on a lecture I attended in which three capital letters (F, M, V) were clearly some very specific implementation in which none of them contain curved edges. I can't find any of them in LaTeX symbol lists or with DeTeXify, but I know I've seen at least some of them before (the V is sometimes used with vector spaces, and each of the letter's usual upper vertices has a horizontal line widening the top), and suspect they're all from the same family. They're not mathbb, mathbf, mathcal, mathfrak, mathit, mathrm, mathscr, mathsf or mathtt characters. The F is similar to a digamma, but with a short line located on and perpendicular to the lower of the horizontal lines; and the M, were it inverted to resemble a W, would have widening lines similar to those of the V.

Answer 1

From the comment discussion, we decided a slab font was the appropriate class. The question arose how to import such glyphs into LaTeX math, if no prior support was available by way of package.

Fortunately, LaTeX supports several slab-serif fonts for text, which means that glyphs from those font families can be imported into math mode.

Here I use the Computer Concrete font (beton package, ccr font family), see http://www.tug.dk/FontCatalogue/computerconcreteeuler/, and import the F, M, and V into math mode as \slabF, \slabM, and \slabV.

\documentclass{article}
\usepackage{mathtools}
\DeclareFontFamily{T1}{ccr}{}

\DeclareFontShape{T1}{ccr}{m}{n}{
  <-8> ccr5
  <8-> ccr10}{}

\DeclareSymbolFont{Xccr}{T1}{ccr}{m}{n}

\DeclareMathSymbol{\slabF}{\mathalpha}{Xccr}{70}
\DeclareMathSymbol{\slabM}{\mathalpha}{Xccr}{77}
\DeclareMathSymbol{\slabV}{\mathalpha}{Xccr}{86}
% =============================================
\begin{document}
$FMV$ versus $\slabF\slabM\slabV$

$\slabF = f(x)$
\end{document}

If no suitable font can be found, and in light of the OP's comment below, there is always the approach of taking a sans font and modifying it. Here, I choose Alegreya, because of its capital M shape. I have also implemented things to satisfy the smaller math styles

\documentclass[12pt]{article}
%\usepackage[T1]{fontenc}
\usepackage{AlegreyaSans}
\usepackage{stackengine,scalerel}

\newcommand\slabF{\mathord{\scalerel*{\stackinset{r}{.2pt}{c}{}{%
  \rule{0.8pt}{2.1pt}}{%
  \fontfamily{\AlegreyaSansfamily}\selectfont F}}{F}}}
\newcommand\slabM{\mathord{\scalerel*{\kern1.5pt\stackinset{c}{}{b}{}{%
  \rule{2.1pt}{0.8pt}\kern6.5pt\rule{2.1pt}{0.8pt}}{%
  \fontfamily{\AlegreyaSansfamily}\selectfont M}\kern1.5pt}{M}}}
\newcommand\slabV{\mathord{\scalerel*{\kern1.5pt\stackinset{c}{}{t}{-.15pt}{%
  \rule{2.1pt}{0.8pt}\kern5.5pt\rule{2.1pt}{0.8pt}}{%
  \fontfamily{\AlegreyaSansfamily}\selectfont V}\kern1.5pt}{V}}}
  \begin{document}
FVM and $FMV$ versus $\slabF\slabM\slabV$

$\slabF = f(x)\cdot \slabM + a\slabV$

$\slabF\slabM\slabV\scriptstyle\slabF\slabM\slabV\scriptscriptstyle\slabF\slabM\slabV$
\end{document}