When signal alterations take place or there's some other need to review the placement of a signal (eg after some SPADs), a signal sighting exercise will take place to review the various risks associated with a signal and things which may affect the time a Driver will need to see it. NR run training courses on signal sighting for people to sit as part of those signal sighting committees, which is what the competence refers to.
Someone who's done a signal sighting course can probably tell you in more detail the specifics of what is covered on them.