Most often the mistakes in the posters are typographical only and more of the spelling mistakes. But some are worse because the mistake is grammar. In the picture is the signage or the Rotary which is a big organization. It makes me wonder why they have that signage with a wrong grammar.
For spelling errors, that is simple to correct since the one who prepared the text would review his work. Aside from that there is an approving person so the errors could be checked. Now when you come out with a poster that has mistakes that only means that you have neglected your job.
Do you make mistakes in your grammar?