One to keep an eye on for the future.
The proposed Institutional Identifiers for libraries and organisations in their supply chain:
http://www.niso.org/workrooms/i2
If this includes museums, it not only gives them a UID, but also, combined with accession numbers, a UID for each object or set of objects.
-- Andy Mabbett @pigsonthewing http://pigsonthewing.org.uk