/usr/share/igtf-policy/classic/18700496.signing_policy is in igtf-policy-classic 1.79-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/igtf-policy/classic/PK-Grid-2007.signing_policy
/usr/share/igtf-policy/classic/PK-Grid-2007.signing_policy