The paper focuses on question about the role of education credentials as a simple and true screening devise of productivity of potential workers. Answering the question we compare private returns to education in unscreened and screened groups of respondents, supposing that in the first case the return to human capital is observed, and in the second — to signals. Insignificant difference of the returns to education for that groups of respondents should be observed if labour market believes the signals. The last comes true for Russia, according to the Mincerian earnings functions estimates made on the RLMS-HSE and NOBUS data sets. Nevertheless as far as particular worker is concerned employer may not believe that education reflects the real productivity correctly and might not pay too much for the signal, increasing contract wage only after some probation period for the employee. Considering the evolution of the return to education with time spent on the same firm we discovered that education as a guaranty of higher earnings is more valuable to female than for male employees.