How to add ISSN metadata to a web page
shkspr.mobi
shkspr.mobi
https://www.bl.uk/help/how-to-deposit-your-digital-publicati...
https://www.crossref.org/documentation/metadata-stewardship/...
"If you publish material on the open web, we should be able to collect this by web archiving. Where a publication is made available online and protected by password or login facility, the Library can request access to archive those materials by giving 1 month’s written notice."
So I guess you would just contact and say "please start archiving my site"?
Just like how you can identify a specific point in a book using ISBN, chapter/section, and page; you identify a specific point in a serial publication using ISSN, the volume/number of the issue, and page.
The ISBN and ISSN serve the purpose of representing the author, title, and publisher. (And in books, also represents the specific edition.)