This is Template:! – the documentation shown below is from Template:!/doc
Use this template instead of
| in a template parameter value.
The bar character (
| also known as pipe) has a special meaning in some circumstances, for example, when used in a template parameter, or when used in a table.
To display a bar, you can always use
| and that is the best solution when you need to display a bar in a template parameter or a table.
However, if you want to define a table in a template parameter then you need a real bar. In that case, you should use this template.
No special template is needed for "
!" (exclamation mark).