- First Q: S/PDIF is not a type of cable or connector, it's a type of digital audio. It can be carried over either RCA ("coaxial" digital audio ports and 2-conductor cables) or over TOSlink (optical digital audio ports and fiber optic cables).
- Second Q: You can tell if it's a TOSlink cable (see below) because that is the only standardized use for that connector and cable, not if it's an RCA cable because RCA connectors/cables can be used for other signals too (although RCA S/PDIF jacks are usually color-coded orange, which helps).
- Third Q: No. RCA is a type of connector (not a type of signal).
RCA connectors/cables are not always analog audio; they are also used for digital audio and a few types of video.
