If you're going to hang these posters on public telephone or power poles you need to comply with the San Francisco Sign Ordinance.
For a summary of San Francisco's guidelines on posting of signs on public property, please visit the Department of Public Works (DPW) web site. The last paragraph provides a PDF file for Posting Signs in San Francisco (PDF) while the text of the statute can be found at: www.amlegal.com under (San Francisco DPW code, Article 5.6)