I'm in Atlanta, Georgia and not familiar with your real estate market in Seattle (although I was born there and used to periodically travel to the area on business ;-)
For the particular neighborhood that you are referring to, do the homes have ample driveway and garage parking? If so, I would not think that speed-bumps, fire lanes and no parking signs have any bearing on the value. However, if there is little to no driveway and/or garage parking, I would tend to believe that these things do impact a properties worth (at least in the minds of home buyers desiring convenient overnight parking).
Ted Shoop - ABR, e-PRO, Realtor
Keller Williams Realty Atlanta Partners