From SA-MP Wiki
When create a string you may find that some character may be impossible or extremely difficult to express in the source code of your script, this is where escape codes come in handy - these allow you to use the symbols and expressions that come under this category. Below is a list of escape codes for the PAWN language.
|Audible beep (on server machine)||\a (also \7)|
|Single quote (')||\'|
|Double quote (")||\"|
|Character code with decimal code "ddd".||\ddd;|
|Character code with hexidecimal code "hhh".||\xhhh;|
The semicolon after the nddd; and nxhhh; codes is optional. Its purpose is to give the escape sequence sequence an explicit termination symbol when it is used in a string constant.
Source: pawn-lang.pdf (pg 99)