As I understand, the "secure" nature of iWatch means that the signature requirement is waived when you pay with it. Regular contactless cards still require you to sign (in the US).
Although this has gotten me looking into what exactly is required to implement mobile payments, and it's given me some clarity. This doc in particular: https://www.uspaymentsforum.org/wp-content/uploads/2019/06/E...
It reads to me like the entity you need an agreement with is a "TSP" (token service provider), and they are at least the sort of organization that you can get a quote from. I don't know if you or the TSP needs an agreement with each bank, but given the relatively slow rollout of Apple Pay support between banks I assume someone somewhere in the chain does.
I can't see the actual specifications though, it costs at least $850/yr as an individual to view them. I did find an old FOSS EMV implementation, but I don't know how much of the spec this implements/what compliance work would be required to use something like it in an actual product: https://github.com/JavaCardOS/OpenEMV
So, thanks for sending me down this rabbit hole. It was somewhat informative at least. :)
