PGP signature of NOC can help you?
The contact information which I only give out directly to other NOCs has NEVER been abused.
Here is the key to this problem. How can you publish contact information in such a way that it only goes to other NOCs. And conversely, how can you ensure that you have access to the contact information of all other NOCs. I suspect that there may be a way for the IP registries (ARIN, RIPE and APNIC) to facilitate this with some kind of replicated database in which change notifications only go out to entities listed in the database. That way every NOC could maintain their own complete copy of a global NOC contacts database and the only need for queries would be to process update notifications and do the occasional resync with the master copy.