20 ECU Vaduz Castle; coloured, piedfort

The ECU was never an official currency of Liechtenstein — the principality uses the Swiss franc — but the early 1990s saw a flood of ECU-denominated collector issues from non-EU states capitalizing on enthusiasm surrounding the Maastricht Treaty, signed in February 1992. Liechtenstein was particularly active in this niche. The piedfort format, doubling the standard planchet thickness, originates in French mint practice dating to the 16th century and was adopted widely by European mints for prestige collector strikes in this period.

The added enamel coloring was applied post-strike, a finishing technique that gained traction in the early 1990s before becoming ubiquitous to the point of tedium.