It is a very interesting question. I am looking into it myself. I am trying to see if volatiles would do the trick. I did not find at the moment any paper answering the question, or at least regarding volatiles. Please let us know if you ever get an answer. If you want to chat a bit more about it or experiments, let me know and we can take it from there.

I do not remember seeing any though I think I remember seeing papers on fruits ripened with and without exogenous ethylene. How are you defining "artificially"? Is it on or off the plant; with or without exogenous ethylene; at ambient or elevated temperature; in the light or in the dark; in a protected (greenhouse) or natural environment? Any why? Is it to verify claims of tree-ripened fruit?

I think 'artificially' mature from Anuj's question is that the fruits are artificially treated with some chemicals to become mature, including the ethylene. There are some fruits have been treated with chemicals to reach their maturity for sale. See the attached article entitled "ARTIFICIAL RIPENING: WHAT WE ARE EATIN". So, in my opinion, a better way to rephrase the question is: to find a biomarker for the fruit ripen trait-- natural ripen vs. delayed ripen (or unripen).

Simply stated: No biomarkers exist, as regardless of what triggers the onset of ripening, the outcome is the same. Of course this is only true for climacteric fruit.

This is a difficult but interesting question.The search for biomarkers is always tough quest and requires patience. I will encourage you to continue your search it will be useful in implementing the organic certification for ripe fruits.

If you can not find a marker among the volatiles or pigments perhaps it might help if you consider looking out for marker proteins (especially functional enzymes proteins), if feasible in your situation. The Proteomic approach (e.g., 2D-PAGE) though tedious initially, might lead you to the identification of differential protein expressions, and the up- or down-regulated protein(s) become/s the marker/s you are looking for.

You might  get more than just a marker if you get interested in the function of the marker protein identified ...

I hope this helps.