Using a blog/forum/site-widget to log URLs of contributions made on other sites is about as tedious as PGP signing contributions. The former seems more authoritative while the latter is complimentary: combined both deter spoofing.
Problems arise as personae increase more so if exposing to the itnerweb. Far less recondite than RealLife name attribution.
Why would anyone want to tie all contributions to ONE id persona or RealLife name? folly!
Self identifying is often insufficient when sharing to public interweb as control of content is relinquished to the other site. Duplicating the contribution and original url on a site I control effects indexing content unmolested in at least one location. If only one location it reveals the contribution was modified- or deleted by the host site. Yes, PGP signing indicates contributions have been modified, but provides no error correction- or restoration facility.
Embedding the URI for duplicate in the PGP signed contribution itself is a second level of deterrent against other claimants. Employing archive.org to that end provides some assurance of longevity. Not yet an iana recognized uri scheme 😉
update: openid is NOT a step in the direction I prefer. Such a “service” is another “all the better to track you my dear” — wolf in Shepard clothing