Although the US Postal Service has a rule against issuing stamps commemorating tragic events, it apparently doesn't prevent them from creating pictorial postmarks.
According to today's issue of the Postal Bulletin, one is coming up that will recognize the 75th anniversary of the loss of the Hindenburg at Lakehurst, NJ:

I thought I'd share the address, as it might be an interesting item to request for those who have interest in postal aviation history.