The mark letter at the end a series is intended primarily to identify to maker in cases of jewellery repairs and modifications. As the letter identifies the maker of the jewellery, it thus allows professional pride in the maker's work.

The last letter of their mark series' are what Auran Kultasepät called 'kretsileima'. The closest translation of this is 'filings mark', specifically the waste filings or rubbish left after making a metal object. They were originally associated with being a mark for identifying the responsibility for shoddy and bad work rather than good; an internal quality or control mark if you like. Only later were these given 'master'-mark status.

In Kultakeskus they call these maker's or 'my own' mark. If this product is found to be plated or ground wrong, it can be returned to the actual maker (= internal control mark).

Turun Hopean used the responsibility mark OMN from 1960 to 1962, when the company was known as Kultasepät Miettinen Nurmi. The OMN mark came from words Olavi Mauno Nurmi. The TH-style symbol characterised by Turun Hopean began use in 1962. The final mark in the series is that of the product designer.