You can find the exact legal regulations in the Civil Code from Art. 720 read up.
For Liechtenstein, the following laws apply to finders:
Art. 191 Property law
If the owner of a lost property cannot be determined, the finder acquires the lost property after five years.
If the item is returned to the owner, the finder is entitled to compensation for all expenses as well as a finder's reward.
In the event of a find in an inhabited house or in an institution serving public use or traffic, the owner of the house, the tenant or the institution shall be deemed to be the finder, but shall not be entitled to a finder's reward.
Art. 69 Ordinance on the Law of Property
The finder's fee is 10% of the value of the lost property.