BAD: I don't think we can do this in a way that is useful and honest.
GOOD: The reason that's the case is that we get so few a year that even a single request that we're not legally allowed to reveal the existence of would result in us giving you fundamentally wrong numbers.
TRYING TO SHOW I'M NOT BEING WEASELLY: I'm happy to share right now, because I'm not prohibited from being totally honest: In the last year, including a sealed inquiry - and I'm comfortable acknowledging its existence because it's pretty public - I think we've had exactly 1.
But I don't want to promise we'll keep sharing these, because our low numbers mean that when even one of ours isn't legally sharable, I know we'll be giving you numbers that are insanely off (on a percent basis), and I'd rather be upfront now about our legal limits than be misleading later.
Some thoughts on the companies above:
I support any effort to be more transparent, but those numbers don't really represent what everyone is terrified of (broad NSA intrusions)
In all cases, it seems like what they're disclosing obviously excludes the NSA type requests we're all really disturbed by. I'm speculating, but the highest account/request ratios on the facebook page are about 2:1 - those are NOT "show us all your metadata" requests; they are "We need to find Grandpa now because he is [off his meds / running a drug cartel]" requests
Assuming these are primarily targeted requests, the large number of them that these companies get makes it easy for them to provide accurate, aggregate data even if some number are under seals (grand jury subpoena's etc.) that prohibit even revealing that they exist
One semi-related note on DMCA notices As of now, we do publicize DMCA requests - we started uploading them a while back, but had some technical issues with Chilling Effects showing them. You should see any new ones going forward though.
Maybe it would be good to implement a warrant canary.
"To date, we have had no requests, check back to see if this notice disappears"
UPDATE: doesn't look like your request is possible: US spy court says internet firms can't report surveillance requests
UPDATE 2: seems that it has happened at least once (emphasis mine):
One slip up was a posting on programmer Q&A site Stack Overflow under the name Ross Ulbricht that asked "How can I connect to a Tor hidden service using curl in php?", before changing the account name to "Frosty". A subpoena by the FBI showed the original account name.