This study aims to examine the formal characteristics of expressions and the trend of the utilization of speech act as shown in 197 public service print advertisements, particularly in its headlines and slogans, from 1983 to 2013 spanning 30 years. According to the study, the endings of headlines were much more likely to be final endings rather than pre-final endings. Headlines with final endings were in the order of descriptive (67.3%) > inquisitive (21.1%) > prescriptive (8.2%) > suggestive (3.4%) forms. Furthermore, the most used speech act in headlines is that of an [argument]. This is a persuasion strategy included in the headline, functioning to ‘weaken the forcefulness’ of a prescriptive order. An [argument] delivers new information from the narrator to the speaker. Moreover, in the process of delivering the information, it guides the listener to solve the problem on their own, thereby weakening the forcefulness compared to a direct [order]. The endings of slogans were also most likely to be descriptive (81.8%). However, compared to the case of headlines, the inquisitive form occurred much rarely. As the purpose of a slogan is to underline the topic and to deliver a clear message to the listener, the inquisitive form is inappropriate. As Lakoff(1973) has suggested on the endings of headlines and slogans as well as on the use of speech acts, it avoids imposing orders but offering options in order to clarify the message and to maintain a civil nature. Though a public service text contains actions that benefits all the constituents of the society, and thereby serve the public interest, it can be seen that a forceful text is not always used to persuade the constituents.