The Joint Declaration was agreed upon at an informal meeting of the European Chiefs of Police in London hosted by the National Crime Agency on 18 April.
Police Chiefs of all EU Member States and Schengen Associated Countries were invited, alongside Europol’s Executive Director.
Here is the declaration (pdf).
That’s true. I guess that in this case, your best bet is (assuming you don’t have something so illegal to hide, that they do want to expend large amount of resources on you) to just go security by obscurity, and have some kind of obscure custom steganography that’s not widely used.
And for PGP - I though that there’s a difference between signing and encrypting a message, and when you only encrypt and don’t sign, they can’t attribute the message to you, assuming they don’t have your private key or the original plaintext? Or is it possible to attribute a encrypted message using only public key and cyphertext?