In 2014 I gave a paper on Women in Numismatics I referred to Christina, and I understood that she left Sweden with her collection when she decamped for The Vatican. It's nice to see something in writing – even though it does not mention a collection. I also understood that she had each piece in her collection stamped with a tiny crowned C. Be grateful to know which is fact and fiction!

Il est rarissime de mettre une contremarque de propriété sur une monnaie de collection, car cela en affecte l'état de conservation6. Un exemple notable est un «C couronné», pas encore identifié, qui a longtemps été considéré à tort être la marque de propriété de la reine Christine de Suède (1632-1654). Curtis L. Clay a argumenté de façon convaincante que cette contremarque n'est pas celle de la reine: en effet, la majorité de ses pièces furent vendues par ses héritiers au Vatican, et nombre d'entre-elles furent confisquées par l'armée napoléonienne et ramenées à Paris, où elles peuvent être identifiées à partir de l'ouvrage Médailles de grand et moyen bronze du cabinet de la Reine Christine de Sigebert Havercamp (La Haye 1742) mais ne sont pas contremarquées. L'hypothèse que cette marque soit celle du roi Charles I d'Angleterre ne semble pas non plus convaincante9, pas plus que celle du poinçon français des objets en mélange cuivreux pour 1745-1749.

It is extremely rare to put a property countermark on a currency of collection because it affects the state of conservation. A notable example is a "crowned C", not yet identified, which has long been wrongly considered to be the mark of property of Queen Christina of Sweden (1632-1654). Curtis L. Clay argued convincingly that this countermark is not that of the queen: indeed, the majority of her pieces were sold by her Heirs at the Vatican, and many of them were confiscated by the army Napoleon and brought back to Paris, where they can be identified from Queen's Medium and Large Medal Medals Queen's Cabinet Christine de Sigebert Havercamp (The Hague 1742) but are not countermarked. The assumption that this mark is that of King Charles I of England does not seem convincing either, nor does that of the French punch objects in copper mixture for 1745-1749.

From: Hadrien Rambach, "A countermarked eagle on a Titus dupondius belonging to the Royal Library of Belgium, sign of provenance from Este to Ferrara ", in Monte Artium, vol. 10 (2017), pp. 103-117

One thing to keep in mind is that you had to be very wealthy in the 17th century to collect.....a king or a queen. It may not belong to Christina or Charles, but certainly to someone of great wealth whose mysterious ego confounds collectors today.