documentclass{memoir}
makeatletter
    usepackage{fouriernc}
    usepackage[scaled=0.82]{luximono}
        usepackage{marvosym,pifont,bbm}
    usepackage[T1]{fontenc}
    usepackage[utf8]{inputenc}
    usepackage[english,slovene]{babel}%
    usepackage{empheq,mathtools,xspace} %
    newcolumntype{C}{>{centeringarraybackslash}X}
    usepackage{tikz}
    usetikzlibrary{shapes,shapes.misc,babel}

    usepackage[many]{tcolorbox}
newtcolorbox{example}[1]{%
    enhanced,
    colback=teal!10, frame hidden, colframe=teal,
    borderline={1pt}{0pt}{teal, sharp corners},
    top=1mm, bottom=1mm, left=1mm, right=1mm,
    enlarge top by=5mm,
    arc=0mm,
    width=textwidth,
    fontupper=smallsffamily,
    overlay unbroken and first={%
        node[trapezium,trapezium left angle=90, trapezium right angle=60,
              fill=teal!60!black,inner xsep=2mm,inner ysep=2pt,yshift=-1pt,
              anchor=bottom left corner,
              text=white,font=smallbfseriessffamily]
        at (frame.north west)
            {#1};},}% end of example

newcommand{T}{ensuremath{text{sffamilyslshape T}}xspace}

newcommand{ud}{;mathrm{d}i}
newcommand{udt}{;mathrm{d}t}
makeatother

    usepackage{microtype}


    begin{document}
%---------------------------------------------------------------%
I like T to be slanted and sans serif character. I use it in text as well in equations:
    [T = a + b quadmathrm{and}quad int_T = cdots    ]
How to achieve this with considering used fonts?

section*{Supplement}
    begin{example}{Transformacija signala $mathrm{Sa}(at)$}
    label{example:uvod.ft-1}
%---------------------------------------------------------------%
Transformacijo pravokotnega pulza preprosto izračunamo z definiciji Fourierove transformacije, v kateri upoštevamo lastnosti simetrij:
    begin{align}
X(omega)   &   = int^{infty}_{infty} p_T exp(-jomega t)udt \
            &   = int^{-T/2}_{T/2} sin(omega t)ud t
                = 2frac{sin(omegaT/2)}{omega}
                = T frac{sin(omegaT/2)}{omegaT/2}
                            notag                                  \
            &   = Tmathrm{Sa}(omegaT/2)
     ,end{align}
kjer je $p_T$ pravokotni pulz.
%---------------------------------------------------------------%
    end{example}

name                                 type              encoding         emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
TAXDKT+CenturySchL-Roma              Type 1            Custom           yes yes no       7  0
MRDFER+SFSI1000                      Type 1            Custom           yes yes no       8  0
TYVRVL+Fourier-Math-Symbols          Type 1            Builtin          yes yes no       9  0
DRJIAH+CenturySchL-Ital              Type 1            Custom           yes yes no      10  0
HDYCOO+Fourier-Math-Extension        Type 1            Builtin          yes yes no      11  0
ZUELID+SFSI0800                      Type 1            Custom           yes yes no      12  0
KPCTUF+CenturySchL-Bold              Type 1            Custom           yes yes no      13  0
LTVCOH+SFSX0900                      Type 1            Custom           yes yes no      14  0
AOTEQD+SFSS0900                      Type 1            Custom           yes yes no      15  0
WSBTSK+Fourier-Math-Letters-Italic   Type 1            Builtin          yes yes no      16  0
YXUCWV+SFSI0900                      Type 1            Custom           yes yes no      17  0