Words, phrases, designs, symbols, letters or drawings that are written, painted or scratched on structures or other items (including but not limited to sidewalks, fences, walls, windows, walls of buildings and trees) are considered graffiti and are in violation of the City's Property Maintenance Code.
To view the actual code text, click on the link below. This takes you to the main page of the MuniCode, click on Chapter 56, then find Section 56-81, subsection (a).