This is such a bad move.
At the Islamic Institute of New York, a mosque and school in Queens, two U.S. marshals rang a doorbell repeatedly, taped a forfeiture notice to the window and left a large document on the ground. A group of men came out and took the document after the marshals left.The damage is done now.
I don't expect to see a response except that everything a US diplomat says to Iranian from now on is the word of a country that pins forfeiture notices on mosques that have no relation at all to any nuclear program or other issue of dispute.
The thing is that the parties don't really need credibility or good faith. Deals can be made up front. For example, in the transfer of low enriched uranium for medical fuel, the fuel can be produced and shipped to a trusted third country at the same time Iran's LEU is shipped. Iran can demand a US commitment to accept Iranian enrichment in advance before making any gestures, commitments or concessions.
But credibility does make things easier. The US has lost a lot with this forfeiture. I could not imagine a worse symbolic statement.