You are entitled to notice of when the restriction is in place. A sign that says "when light flashing" or "when children present" is probably sufficient.
The law does require sufficient notice of when you are entering a school zone. Most of the time, this is from a posted sign indicating either the times the school zone is in effect or an indication of when lights are flashing, children present, etc.
I agree with all prior counsels answers. I have printed below some of the applicable Federal Way ordinances.
8.05.090 Authority for local use of automated safety cameras.
(1) Automated traffic safety cameras may be used to detect stoplight or school speed zone violations. This section is intended to provide authorizing language as required under RCW 46.63.170.
(2) Use of automated traffic safety cameras is restricted to two-arterial intersections and school speed zones only.
(3) Automated traffic safety cameras may only take pictures of the vehicle and vehicle license plate and only while an infraction is occurring. The picture must not reveal the face of the driver or of passengers in the vehicle.
(4) All locations where an automated traffic safety camera is used must be clearly marked by placing signs in locations that clearly indicate to a driver that he or she is entering a zone where traffic laws are enforced by an automated traffic safety camera.
(5) For the purpose of this section, “automated traffic safety camera” means a device that uses a vehicle sensor installed to work in conjunction with an intersection traffic control system or a speed measuring device, and a camera synchronized to automatically record one or more sequenced photographs, microphotographs, or electronic images of the rear of a motor vehicle at the time the vehicle fails to stop when facing a steady red traffic control signal or exceeds a speed limit in a school zone as detected by a speed measuring device.
(6) Nothing in this section prohibits a law enforcement officer from issuing a notice of traffic infraction to a person in control of a vehicle at the time a violation occurs under RCW 46.63.030(1)(a), (b), or (c).
(7) This section shall be applied as prescribed by RCW 46.63.170.
(8) Violations detected through the use of an automated traffic safety camera shall be issued with a monetary penalty equal to the same total penalty issued for such violations if detected by an officer without the use of an automated traffic safety camera, including the base penalty plus any statutory assessments authorized under state law, as set by the state supreme court, statute, or other court rule. However, in no case shall such penalties be issued in an amount that exceeds the amount of a fine that may be issued for an infraction involving a parking violation and shall be processed in the same manner as a parking infraction. Such infractions may be issued with a penalty up to the maximum fines allowed for parking infractions, which are up to the amounts authorized pursuant to FWRC 8.05.040 and 8.05.100.
(Ord. No. 09-613, § 1, 6-2-09; Ord. No. 05-508, § 7, 11-1-05. Code 2001 § 15-14.)
8.05.100 Violations as traffic infractions.
Failure to perform any act required or the performance of any act prohibited by this title or an equivalent administrative regulation relating to traffic, including parking, standing, stopping, and pedestrian offenses, is designated as a traffic infraction unless otherwise provided, except violations of Chapter 8.10 FWRC, Commute Trip Reduction (CTR) Plan; violations of Chapter 8.15 FWRC, Impoundment for No License; and violations of Chapter 8.25 FWRC, Bicycles, which are as provided therein.
(Ord. No. 09-597, § 38, 1-6-09. Code 2001 § 15-15.)
If you check the sign it probably states "when lights are flashing". The times that they are scheduled are set by the individual school. These schedules can be found on the city of Federal Way website. I have had some success recently with these offenses in Federal Way. Give me a call.