[latchkey]

A very long time ago, HP made a GPS time card just like this, encased in glass and filled with an inert gas such that if the card was tampered with, it was rendered useless.

This prevented someone from faking the time signal.

[audiometry]

Someone send one of these to CuriousMarc — he is peerless in working on these vintage high precision test pieces.

[BonoboIO]

Can you show us a picture. Did not find anything on google beside HP Laptop spam.

[latchkey]

I'm not sure it was ever sold to the public.

Buddy of mine owns timestamp.com and we were building a service where you could hash/timestamp emails (we would take over the MX for a domain and become a forwarding service). All of this was long before we had blockchains.

Sadly, it never really took off so we abandoned the idea (what is up there now is currently another half attempt at the idea).

Others have tried, but it isn't really a huge demand despite the apparent need.