\documentclass{article}
\usepackage{amssymb}
\begin{document}
\textsc{Text in Small Caps using TEXTSC}

{\scshape Text in Small Caps using SC\itshape bonga}

mathrm : $\mathrm{ABCXYZ}\mathrm{abcxyz}$

rm : ${\rm ABCXYZ}{\rm abcxyz}$

mathit : $\mathit{ABCXYZ}\mathit{abcxyzc}$

it : ${\it ABCXYZ}{\it abcxyz}$

SIMPLE : $ABCXYZabcxyz12345$

%mathtt : $\mathtt{ABCXYZ}\mathtt{abcxyz}\mathtt{12345}$

%mathbb : $\mathbb{ABCXYZ}$

%mathcal : $\mathcal{ABCXYZ}$

%mathfrak : $\mathfrak{ABCXYZ}\mathfrak{abcxyz}$

mathbf : $\mathbf{ABCXYZ}\mathbf{abcxyz}\mathbf{12345}$

bf : ${\bf ABCXYZ}{\bf abcxyz}{\bf 12345}$ 

%mathsf : $\mathsf{ABCXYZ}\mathsf{abcxyz}\mathsf{12345}$

underline : $\underline{\sigma}$

overline : $\overline{\frac{\pi}{2}}$

underline and overline in display : $$\underline{\rho} \overline{\frac{\theta}{2}}$$
%$\hat{\frac{\pi}{2}hat} \widehat{widehat}$

\end{document}