The Manager of the Yakima City Codes Department says since it's the political season they're watching where campaigns are placing signs. Joe Caruso says signs can't be affixed to any city property. That means political signs can't be on city fences or utility poles or in city parks. The signs can however be placed on public rights-of-way next to parks. Caruso says they can't be everywhere so they rely on citizen complaints to find illegally placed signs.

A news release from the city of Yakima gives more details and rules about political signs.
"Temporary signs can be no larger than four square feet and the height cannot exceed three feet, including the stake.
    Temporary signs may be placed on public rights-of-way between the curb and property line. However, the abutting property owner’s approval is required, and no signs are allowed to block the clear view triangle.
    Dilapidated or nuisance signs in rights-of-way must be removed

To ensure campaign signs follow the sign code rules and regulations, candidates are encouraged to read Yakima Municipal Code section 15.08."