/usr/share/igtf-policy/classic/SiGNET-CA.namespaces is in igtf-policy-classic 1.59-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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#NAMESPACES-VERSION: 1.0
#
# @(#)3d5be7bc.signing_policy.namespaces
# CA alias    : SiGNET-CA
#    subord_of: 
#    subjectDN: /C=SI/O=SiGNET/CN=SiGNET CA
#    hash     : 3d5be7bc.signing_policy
#    (generated automatically from 3d5be7bc.signing_policy)
#
TO Issuer "/C=SI/O=SiGNET/CN=SiGNET CA" \
  PERMIT Subject "/C=SI/O=SiGNET/.*"
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