When transcluded e.g. at https://wikimediafoundation.org/wiki/WPZeroPetition petitions always give the message "You cannot sign this petition because you are currently blocked." This occurs even when logged out.
It is still possible to view and sign at the Special page directly e.g. https://wikimediafoundation.org/wiki/Special:Petition/WPZero
No idea how long this has been broken. Looks like the last petition signature was 26 July, and the last signature on the WPZero petition was 21 February.