Turkey has gone through series of legal, political, cultural, economical changes after the declaration of republic in 1923 by Mustafa Kemal Ataturk. The founder of Turkish republic, Ataturk (literally means Turkish father) became the first leader in Europe who gave suffrage to women.
During the Ottoman times women had to wear hijab and had very limited rights in different fields of life. After republic they were no longer obligated to wear head scarves. Many schools and faculties opened to female students.
Ataturk promoted women to study and participate actively in the labour force of the country. However wearing head scarves are left to women choice.
While in the big cities ratio of the women wearing head scarves is low, in the countryside it is higher. Since it is a personal choice, there is no difference between the women who wear and who don’t. Even in one family, while the mother may wear, instead the daughter may not. It is not a sign of religion, social class or religious group in the country.
Also the women without headscarf may wear when they visit a mosque or attend a religious ceremony as a sign of respect.
Women traveler in Turkey, no need to hijab. You can dress how ever you are in your normal life.