TWiki defines some standard special tokens that can be used to replace characters in some parameters - notably those to FormattedSearch and IfStatements - to defer evaluation of the parameter until later. These special tokens are often called "escapes", because they allow the character to "escape" from its normal meaning.
$n or $n()
New line. Use $n() if followed by alphanumeric character, e.g. write Foo$n()Bar instead of Foo$nBar
$nop or $nop()
Is a "no operation". This variable gets removed; useful for nested search
$quot
Double quote (") (\" also works)
$percnt
Percent sign (%)
$dollar
Dollar sign ($)
If you ever find yourself needing to escape an escape, you can use $dollar to escape the leading dollar, thus: $dollarpercnt.