Which country is known by the initials H.C. and what do these intials represent?

https://www.diyfamilylawaustralia.com/pages/child-issues/list-of-hague-convention-countries

H.C. stands for the Hague Convention, and an H.C. country is one which has signed up for this convention which among other things appears to give protection for children at risk of being abducted by an estranged parent from another country.

You could be referring to Switzerland, which is known as Confoederatio Helvetica. I suppose that this could also be turned around to be the Helvetic Confederation, from which would you glean the letters H.C.

https://en.wikipedia.org/wiki/Switzerland

The other two countries that spring immediately to mind are Greece (known as Hellas, although in Greek it would be called E.D) and Croatia (known as Hrvatska, although this would be R.H in Croat).