/usr/include/sigx-2.0/sigx/ is in libsigx-2.0-dev 2.0.2-5ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/sigx-2.0/sigx/auto_dispatchable.h
/usr/include/sigx-2.0/sigx/auto_tunneler.h
/usr/include/sigx-2.0/sigx/bad_caller.h
/usr/include/sigx-2.0/sigx/bad_dispatcher.h
/usr/include/sigx-2.0/sigx/bad_sync_call.h
/usr/include/sigx-2.0/sigx/choose_lock.h
/usr/include/sigx-2.0/sigx/connection_handler.h
/usr/include/sigx-2.0/sigx/connection_wrapper.h
/usr/include/sigx-2.0/sigx/const_trait.h
/usr/include/sigx-2.0/sigx/dispatchable.h
/usr/include/sigx-2.0/sigx/dispatcher.h
/usr/include/sigx-2.0/sigx/fwddecl.h
/usr/include/sigx-2.0/sigx/glib_auto_dispatchable.h
/usr/include/sigx-2.0/sigx/glib_dispatcher.h
/usr/include/sigx-2.0/sigx/glib_lockables.h
/usr/include/sigx-2.0/sigx/glib_threadable.h
/usr/include/sigx-2.0/sigx/internal_types.h
/usr/include/sigx-2.0/sigx/lock_acquirer.h
/usr/include/sigx-2.0/sigx/lockable.h
/usr/include/sigx-2.0/sigx/lockable_fwddecl.h
/usr/include/sigx-2.0/sigx/locking_dispatcher_ptr.h
/usr/include/sigx-2.0/sigx/manual_dispatchable.h
/usr/include/sigx-2.0/sigx/nonassignable.h
/usr/include/sigx-2.0/sigx/noncopyable.h
/usr/include/sigx-2.0/sigx/nonheapallocatable.h
/usr/include/sigx-2.0/sigx/noninstantiatable.h
/usr/include/sigx-2.0/sigx/nonpointeraliasing.h
/usr/include/sigx-2.0/sigx/operator_new.h
/usr/include/sigx-2.0/sigx/ref.h
/usr/include/sigx-2.0/sigx/request_f.h
/usr/include/sigx-2.0/sigx/shared_dispatchable.h
/usr/include/sigx-2.0/sigx/signal_f.h
/usr/include/sigx-2.0/sigx/signal_f_base.h
/usr/include/sigx-2.0/sigx/signal_source_base.h
/usr/include/sigx-2.0/sigx/signal_source_func.h
/usr/include/sigx-2.0/sigx/signal_source_obj_mem.h
/usr/include/sigx-2.0/sigx/signal_source_threadprivate.h
/usr/include/sigx-2.0/sigx/signal_traits.h
/usr/include/sigx-2.0/sigx/signal_wrapper.h
/usr/include/sigx-2.0/sigx/signal_wrapper_base.h
/usr/include/sigx-2.0/sigx/sigx.h
/usr/include/sigx-2.0/sigx/static_assert.h
/usr/include/sigx-2.0/sigx/threadable.h
/usr/include/sigx-2.0/sigx/tunnel_base.h
/usr/include/sigx-2.0/sigx/tunnel_context.h
/usr/include/sigx-2.0/sigx/tunnel_context_base.h
/usr/include/sigx-2.0/sigx/tunnel_functor.h
/usr/include/sigx-2.0/sigx/tunnel_validity_tracker.h
/usr/include/sigx-2.0/sigx/types.h
/usr/include/sigx-2.0/sigx/validity_trackable.h
/usr/include/sigx-2.0/sigx/volatile_trait.h