For anyone interested, this is the website that has images of Codex E, a copy of Acts that has Latin in one column with the corresponding Greek on a second column. The codex is thought to be from the mid 6th century to the early 8th. Enjoy!
1: OThC, OThY etc with a superlinear line over the ThC (Th is Theta) seems to always be used and is translated as Deus though I have never seen it abbreviated this way before as it is usually ThC, ThY... with a superlinear line over the whole abbreviation.
2: OIC is sometimes used with a superlinear line over the IC but is inconsistent, with IC, IY, IN with a superlinear line over the whole abbreviation preferred and is translated as Ihesus, Ihesum.....
3: So far it seems that KC, KY, with a superlinear line over the abbreviation is only used and is translated as Dominus, Dominum...
OPiHP (Pi = Pi) is being used with a superlinear line over the PiHP (Pi, Eta, Ro) and is translated as Pater (Father) which is the Greek word as well. It's usage in this case is in reference to God (God the Father). It's starting to look like any mention of God is started with an O as part of the abbreviation for some reason ie OThC, OPiHP. But why then is IC only rendered as OIC some of the time with IC, IY... so far, being the norm?
For anyone who wants to see how Kirios/Dominus is used, in Acts anyway, to refer to God or IC or whatever, studying this codex is a must. If the O in front of an abbreviation is an indicator that God is being referred to, and that seems to be the case, then this is a quick and simple guide as to how Kirios/IC/God is being handled.