The first of these Claudian letters is the antisigma.
Open o looks like a reversed letter 'C'. Claudiusintroduced a Ɔ (the antisigma) with the intention of replacing bs and ps.
Definition from Aasen (1873), Norsk ordbog med dansk forklaring, showing the Danish explanatory symbol “ɔ:”.
The Scandinavian explanatory symbol (forklaringstegnet) can be typeset using the open o followed by a colon, thus: ɔ:. It is used to mean "namely", "id est", "scilicet" or similar.[4]
This letter is often used to refer to the Copyleft official sign, which looks like an open o with a circle around it.