The German one can be produced with the wasysym package. More precisely, if loaded without arguments, then the package provides a \varint command for the upright integral. If loaded with the integrals option, it overrides the normal \int command.
The integrals from mathabx (it redefines \int) are beckwards slanted when used in inline style and upright when in display style.
(Generally if you look for a symbol, detexify and the comprehensive symbol list are of invaluable help.)
The amsmath package provides the \overset and \underset macros that can be used to place one symbol above or below another. If you want text above and below, you could use \DeclareMathOperator* (also from amsmath).
\documentclass{minimal}
\usepackage{amsmath}
\DeclareMathOperator*{\eq}{=}
\begin{document}
\begin{equation*}
\underset{b}{=} \quad \eq^a_b
\end{equation*}
\end{document}
There shouldn't be any problems using this in amsmath environments such as align.
\begin{align*}
A &\eq^b_a B \\
&\eq^b_a C
\end{align*}
However, if you use it in the middle column of an eqnarray or eqnarray* (which are generally considered to be obsolete), then you will need \displaystyle before \eq.
All of the above applies to egreg's suggestion of defining \eq via
\newcommand{\eq}[2]{\mathrel{\operatorname*{=}_#1^#2}}
which seems to improve the spacing (and may be better in other ways as well).
Best Answer
Brew your own, made scalable. If the default sans font changes, some adjustments may be needed to the measurements.
If one prefers a less bold version