Register your work with the Library of Congress. I have been doing that for all my work since 2010. Each year, the process seems to be more complex and costlier, but your work is your legacy and the last Supreme Court ruling states that an issued registration is required for the pursuit of litigation.
With that being said, I have been on Board of Directors for two large NY camera groups and when polled, 90% of members do not register. Folks lament about infringement, but don’t take their craft seriously enough, and/or get defeated by the cost and copyright legalese process.
Signing Print Work
There is no standard process but at a minimum Sign your work, with archival pigment .02 and no greater than .05 ink (Pigma Micron), on the far right bottom side, on the print border , between matte. Put a label on the back of the print with your name, address, phone, email, site, LOC registration#, the title of print, date, and edition serial # of #.
Perhaps a good place to find out how photography fine artists sign their work is to go to an art gallery or art center/museum. You may want to reach out to member Alain Briot for advice or tour his website and see if he’s made a blog on the subject. I believe he’s going to be on NPS QA next month.