$re = '/SN=([A-Z]+:[\d-]+):/';
$str = 'SIGN="000F 0E70 FA83 B72F D215 C7EE 4AF4 6440 A547 12B1 0603 \\
SN=RK:7573-0:2832397:369963
1086 0857 BFF1 5FC2 CE6F C87D 7C00 DF64 C1AD DD39") }';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php