@ character before a function call

It silences errors and warnings. See Error Control Operators.

As already answered the @ will stop the error (if any) from showing up.
In terms of performance this is not recommended.

What php is doing is:

• reading the error display state
• setting the error display to show no errors
• running your function
• setting the error display to it's previous state

If you don't want any errors showing up use error_reporting(0);.

Or just write bug free code :P

the "@" will silence any php errors your function could raise.