Can you apply schema to a newsletter signup link?

[RosemaryB]

I was curious if it is possible to markup a newsletter signup link for a client.  If yes, what schema property should I use?  https://schema.org/Action?

[Mobilio]

Yes, there are 4 Schema.org objects:
https://schema.org/SubscribeAction
https://schema.org/RegisterAction
https://schema.org/JoinAction
https://schema.org/FollowAction

There is only one issue - on all of them there is "agent" that we're talking about. Like "John join ACME", "John registered to ACME", etc. And without agent codes can be verified w/o issues but look meaningless "join ACME", "registered to ACME", etc.

I also try to implement Join/Subscribe/Register as SiteLink:
https://developers.google.com/structured-data/slsb-overview
but can't pass validation because "query-input". If exist it's unknown for subscribing, if i delete it it's missing and required. So consider both ways as broken currently.

Anyway - you can markup emails:
https://moz.com/blog/markup-for-emails
and make them little bit actionable.