How/Where to find such special symbol/character?

Question

I am developing a mobile app. In this app, I need some special characters and symbols, e.g. θ, ʒ, ʃ, dʒ, t͡ʃ I have found all I need except one symbol.

How can I write (or where can I find) a letter like that:

And also I want to know what is the best way of searching such symbols. What are they called?

Note: The symbol I look for is not single character. I might be able to use it as I use ^ symbol (like â, ê). What I mean is singleton symbol does not work in my case. The symbol should be secondary symbol along with the letter.

Any help would be much appreciated.

Answer 1

Those symbols are in IPA:

\documentclass{article}
\usepackage{tipa}

\begin{document}

\textsubbridge{t}\quad
\textyogh\quad
\textesh\quad
\textdyoghlig\quad
\textteshlig

\end{document}

For the last one you might prefer

\texttoptiebar{t\textesh}

The characters are available in some OpenType fonts, for example FreeSerif. Compile the following with XeLaTeX or LuaLaTeX

\documentclass{article}
\usepackage{fontspec}
\setmainfont{FreeSerif}

\begin{document}

\textsubbridge{t}\quad
\textyogh\quad
\textesh\quad
\textdyoghlig\quad
\textteshlig\quad
\texttoptiebar{t\textesh}

\end{document}

Answer 2

Build your own. The parameters \rlwd and \rldp can be changed, as well as the 1pt underset gap.

\documentclass{article}
\usepackage{calc,stackengine}
\def\rlwd{.5pt}
\def\rldp{.3ex}
\def\underframe#1{\stackunder[1pt]{#1}{\rule[-\rldp]{\rlwd}{\rldp}\kern-\rlwd%
  \rule{\widthof{#1}}{\rlwd}\kern-\rlwd\rule[-\rldp]{\rlwd}{\rldp}}}
\begin{document}
This is a \underframe{t} and \underframe{A}.
\end{document}

Here it is with \def\rlwd{.3pt} and \def\rldp{.4ex}:

If you found the underframe too wide, you could replace in the definition {\widthof{#1}} with {\widthof{#1}-1pt}, for example, obtaining something that doesn't overhang the serifs.