In the US, as anyone can get a Diamond with their co-branded CCs, nothing special was given. No welcome gifts or anything like that compared to outside of North American Hilton(s). No acknowledgement of status - assume the upgrade was given only due to booking through AMEX's FHR programme. The upgraded room was on the 46th Floor, and the views were decent but nothing to ring special about. Quite a walkable distance between places within NYC.