Let's say you cannot find the symbol you need anywhere. You can create a custom symbol. For example, the code
\documentclass{article}
\usepackage{graphicx,amsmath,amssymb}
\DeclareRobustCommand{\diamondtimes}{%
\mathbin{\text{\rotatebox[origin=c]{45}{$\boxplus$}}}%
}
\begin{document}
$a\diamondtimes b$
\end{document}
creates and calls a symbol, giving
This is a simpler example; it merely has to rotate an already existent symbol. However, you can create more complex symbols.
This section is in the process of being expanded.