I reached out to a historian at the National Register of Historic Places (which was created through the NHPA) and they told me that neither of those associations have ever used a sticker like that. I also reached out to a friend who works with antique furniture and they said that they've never seen it before, but that they think it's likely that my bar could have come from a hotel. Now I'm brainstorming what else the NHPA acronym could mean...could the 'H' stand for hotel, housing; 'P' for protection? Any ideas? Would be a perfect little exercise for someone who loves riddles haha