Unknown foreign ribbon of Vizeadmiral Erhard Maertens

[Kriegsmarine Admiral]

- Eisernes Kreuz (1914) 2. Klasse

- Hamburgisches Hanseatenkreuz

- Großherzoglich Oldenburgisches Friedrich August-Kreuz 2. Klasse mit Spange “Vor dem Feinde”

- Ehrenkreuz für Frontkämpfer

- ???

Does anyone recognize the last ribbon?

At first glance, the last ribbon looks like the k.u.k. Österreichisches Militär-Verdienstkreuz 3. Klasse mit der Kriegsdekoration. But that award is not listed for Maertens in any of the Rangliste. Other ribbon with a similar device, Kaiserlich Türkischer Eiserner Halbmond is also not listed. And I don't think it's the Ehrenzeichen des Deutschen Roten Kreuzes either. Perhaps someone will have an idea. It could be a foreign award with this kind of circle device. Member of the forum "P.F." suggested something from South America from the 1920/1930s. There is also an possibility it's indeed the Österreichisches Militär-Verdienstkreuz 3. Klasse mit der Kriegsdekoration that was somehow left out of the Rangliste for Maertens.

Any help is appreciated.