 In older works in the 1950s the signature is mostly and traditionally written in plain letters with the date as for example in the 1955 signature.In this 1954 example it is etched as 'O ai'.With arrival of the rainbow period in the 1980s some new signature is introduced where the O encircles the other letter in a cartouche-like manner like in this example of 1985 on one of the large 96 gradations work.