Detecting pkgsrc install (ocsinventory-agent)

[David Brownlee <abs%absd.org@localhost>]

net/ocsinventory-agent provides system inventories, including
installed packages. The various backends tag installed packages as
coming from 'deb', 'rpm', 'ByHand' or, for the output from pkg_info
''. It would be nice to be able to identify pkgsrc from other pkg_info
commands, potentially by running a specific pkg_admin or other
command.

The specific use case is on a RedHat ES server where pkgsrc is used to
provide up to date perl and other packages without impacting the base
RPM installs.

So, does anyone how of a simple command option to differentiate
installed pkgsrc tools from Open or FreeBSD tools, or would it make
sense to provide one? Note, I do not want to use OS as pkgsrc is
multiplatform, and would prefer to avoid checking for /usr/pkg as
admins can reasonably alter that