/usr/share/php/ProxyManager/Signature/ is in php-proxy-manager 2.0.0-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/ProxyManager/Signature/ClassSignatureGenerator.php
/usr/share/php/ProxyManager/Signature/ClassSignatureGeneratorInterface.php
/usr/share/php/ProxyManager/Signature/Exception/
/usr/share/php/ProxyManager/Signature/Exception/ExceptionInterface.php
/usr/share/php/ProxyManager/Signature/Exception/InvalidSignatureException.php
/usr/share/php/ProxyManager/Signature/Exception/MissingSignatureException.php
/usr/share/php/ProxyManager/Signature/SignatureChecker.php
/usr/share/php/ProxyManager/Signature/SignatureCheckerInterface.php
/usr/share/php/ProxyManager/Signature/SignatureGenerator.php
/usr/share/php/ProxyManager/Signature/SignatureGeneratorInterface.php