As you may know, modern day unclaimed property laws are a descendant of an ancient common law legal doctrine known as bona vacantia ("vacant goods," in latin). Under this doctrine, items of personal property with no known owner were deemed to be the property of the sovereign. (The term escheat, though often used in the context of unclaimed personal property, is actually a misnomer; the common law doctrine of escheat actually referred to ownerless "real" property (i.e., land) not personal property). While today's unclaimed property (US) and bona vacantia (UK) laws are primarily addressed towards unclaimed intangible property (e.g., money, deposits, checks, wills, etc.) it is worth noting that the original concepts of bona vacantia and treasure trove are alive and well in the UK.
For example, the BBC News reported yesterday on Scotland's 330 "treasure trove" cases over the past year - situations where archaeologists and/or ordinary citizens found medieval rings, ancient weapons, and other artifacts. As the article explains, "[u]nder Scottish law, the Crown has the right to all lost and abandoned property which is not otherwise owned. Finders have no ownership rights and must report any objects to the treasure trove unit." Such items are reported and turned over to the Queen and Lord Treasurer's Remembrancer.
Included in last year's findings was an axe head believed to be between 4 and 6 thousand years old. There was no word on whether 4,000 years of penalties and interest would be assessed for late reporting.