If any employer, during the continuance of a strike, lockout or other labor trouble among his employees publicly advertises in newspapers, or by posters or otherwise, for employees, or by himself or his agents solicits persons to work for him to fill the places of strikers, he shall plainly and explicitly state, in such advertisements or oral or written solicitations, that a strike, lockout or other labor disturbance exists. If a strike exists, the employer shall in the advertisement plainly and explicitly state that a “strike” exists.