Usually letters like that inside of a ring are makers marks or initials of the people for whom the ring was made. If a mark is right next to a karat mark it could tell us something about the gold itself. A ring marked 10k EPN would mean 1ok gold electroplated to nickel base metal. That item is not real gold.
The initials SWL mean Safe Working Load
These are the designers initials.
Millimolar
Type of computer networks: 1.)LAN. 2.)WAN. 3.)WLAN. 4.)MAN. 5.)SAN. 6.)EPN. 7.)RAN. 8.)EPN. 9.)VPN. Are the most important of using computer networks.
KC is the initials of his FaceBook account, apparently.
If you mean the international car registration then it is Switzerland
tgat
If you mean initials, then they are HI.
Makers initials
Initials of the maker.
I hope you mean 'What do the initials 'UN' mean - United Nations.