You have the right answer in your post.

Originally Posted by: mmatwyuk

(other than a point of refernce i.e 3rd , 5th, 7 th etc. fret)

That's all. It's simply a quick handy visual reference point. Classical guitars traditionally do not have fret markers or dots on the fretboard, but they do usually do have them on the edge of the bass side of the neck for the player to see.

Interestingly, custom Gibsons sometimes have a 1st fret marker!

https://en.wikipedia.org/wiki/Gibson_Les_Paul#/media/File:Gibson_Les_Paul_54_Custom.jpg