While not part of the Public Access Policy, note that NIH also requires grant acknowledement in the media (e.g., press releases, web stories, blog posts).
Grantees are required to include the following:
The NIH Public Access Policy ensures that the public has access to the published results of NIH funded research. Effective April 7, 2008, the NIH Public Access Policy requires that all peer-reviewed articles arising from NIH funds are submitted to PubMed Central upon acceptance for publication.
To help advance science and improve human and animal health, the Policy requires that these papers are accessible to the public in PubMed Central no later than 12 months after publication.
NIH further requires investigators to include the PubMed Central reference number (PMCID) in all subsequent NIH grant applications, proposals, and progress reports as evidence of compliance.
NIH Public Access Policy Fact Sheet (Feb 2012) discusses the implications of the policy.
A (not so) friendly reminder: NIH will delay processing of non-competing continuation grant awards if publications arising from that award are not in compliance with the Public Access mandate. NOT-OD-12-160 (Nov 2012)
Changes to the NIH Public Access Policy and the Implication (Jan 2013 Webinar from NIH)