After some digging, it seems there is no documented way of tagging lifeboat stations and lifeboats. Tagwatch also didn't turn up anything especially obvious, so I've created a tagging proposal:

osm.wiki/index.php/Proposed_features/Lifeboat

I've tagged the Horton lifeboat station in accordance with this proposal. I may contact the RNLI to see if they will provide a copyright-free list of lifeboat stations and their locations (although I suspect they won't have the lat/lon for them all :( ).