Cr. 106/6a Ex. RBW collection, Ex. Crédit Suisse(a.k.a Schweizerische Kreditanstalt) List 52, January 1988, 422.
Of interest: The catalog listing scanned above is from RBW's own copy of this catalog which was scanned for me by a very nice member over at FORVM. RBW bid on and bought 9 coins from this catalog in January of 1988 at an exchange rate of ~$.75 USD/CHF and won this particular coin at 300 CHF($225 USD)