I write songs for guitar and voice. Let's say for a particular song, I put the capo on the 2nd fret because this is what fits my vocal range for the melody. For another person, it could be the 3rd fret, or no capo. How do I indicate in the score to the player to put the capo wherever suits them best?
The key that a piece of music is performed in is often determined by the singer — their part being the most important, and the best part of their range often the least flexible. The rest of the performers will have to transpose the music to suit.
Fortunately, for a guitar player (reading tablature) this is rather trivial (by simply adjusting the position of a capo).
This practice is so commonplace that it doesn't need to be explicitly endorsed on the score, and so no notation for this is necessary.
Use of capo varies between putting it on a certain fret because the player knows exactly why it has to go there - and which chord shapes will have to be used consequently, and 'I put it there because someone told me to'.
To cover both ends of this spectrum, it's worth writing the actual chords, as far as concert pitch is concerned - in other words, a good guitarist will be capable of choosing which inversion they use. And, writing in, say, "2nd fret capo", with the appropriate chord shapes that that position will achieve. Write one on top of the other, or concert followed by capo'd in brackets, with a suitable legend at the beginning.