All the codes cited in sherry's posting above are reproduced below. They are not applicable. This issue was adjudicated in SANCTITY OF HUMAN LIFE NETWORK v. CHP where it states that:

--As noted, the CHP has terminated plaintiffs' activities on freeway overpasses under the purported authority of sections 21465 and 21467. The CHP officers who testified at trial stated they would continue to remove prohibited signs in view of freeway motorists under this authority, although the officers were less than clear concerning what is a prohibited sign. Plaintiffs assert these Vehicle Code sign statutes do not apply to their signs. After consideration of the statutes, their context within the Vehicle Code, and their legislative history, we agree with plaintiffs that sections 21465 and 21467 do not apply to their signs.--
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--During trial, the CHP's expert on the Vehicle Code, Officer Scott Hall, who teaches the Vehicle Code at the Highway Patrol Academy and is authorized to speak authoritatively concerning the meaning of the Vehicle Code for the CHP, testified concerning the CHP's enforcement of section 21465. His testimony reveals that the CHP does not have a clear or articulable definition of the scope of section 21465.--
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--The CHP's view is that bus advertising and bumper stickers do not violate section 21465. When asked why that is so, the officer replied: "You got me."--
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--The plain meaning of "unofficial sign," taken out of the context of the statutory scheme relating to traffic signs, might suggest that the statute refers to any sign, traffic related or not, that was not placed there by the government. While the plain meaning, without consideration of the context, may lead to this interpretation, other canons of statutory interpretation preclude this interpretation.--
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--It cannot be seriously argued that the Legislature intended to prohibit any unofficial sign in view of a roadway. This would include billboards, house numbers, bus advertising, bumper stickers, and a host of other signs that are everywhere to be found in view of roadways. The prohibition in section 21465 bears no contextual relation to state statutes and local ordinances concerning private signs.--
&, finally,
--Accordingly, the legislative history of section 21465 is consistent with what we have concluded is the statute's reasonable interpretation -- that is, that it applies only to traffic signs and was never intended to do more. Plaintiffs' signs cannot be characterized as traffic signs subject to prohibition under section 21465. They did not purport to be traffic signs. They did not imitate or resemble traffic signs. The signs did not attempt to direct the movement of traffic or hide from view any traffic sign. The CHP, relying only on sections 21465 and 21467, cannot prevent plaintiffs from displaying the signs.
Plaintiffs have presented an actual controversy concerning whether the CHP may interfere with plaintiffs' activities under the authority of sections 21465 and 21467. We conclude the CHP may not do so. Therefore, plaintiffs are entitled to declaratory relief on that issue.--

Isn't the law fun? Again, it seems to me that 2410 is the only section that applies, and that section can only be used on a case by case basis. CHP cannot issue a blanket prohibition on private signs held on overpasses. Apparently they have to make some sort of determination on the scene as to whether traffic flow is being impacted, and then issue a lawful order. If the sign holders come back in an hour, or a day, or a week, a new determination has to be made all over again regarding traffic flow at those new times. How that determination is made doesn't seem to be at all clear, and apparently is solely at the CHP officer's discretion.

This is why it seems to me that a legal challenge will be necessary to clarify the issue. Lawyers really need to step forward on this...

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Unauthorized Traffic Devices
www.dmv.ca.gov/pubs/vctop/d11/vc21465.htm
21465. No person shall place, maintain, or display upon, or in view of, any highway any unofficial sign, signal, device, or marking, or any sign, signal, device, or marking which purports to be or is an imitation of, or resembles, an official traffic control device or which attempts to direct the movement of traffic or which hides from view any official traffic control device.

Light Preventing Recognition of Official Traffic Control Device
www.dmv.ca.gov/pubs/vctop/d11/vc21466.htm
21466. No person shall place or maintain or display upon or in view of any highway any light in such position as to prevent the driver of a vehicle from readily recognizing any official traffic control device.

Light Impairing Driver's Vision
www.dmv.ca.gov/pubs/vctop/d11/vc21466_5.htm
21466.5. No person shall place or maintain or display, upon or in view of any highway, any light of any color of such brilliance as to impair the vision of drivers upon the highway. A light source shall be considered vision impairing when its brilliance exceeds the values listed below.
The brightness reading of an objectionable light source shall be measured with a 1 /2-degree photoelectric brightness meter placed at the driver's point of view. The maximum measured brightness of the light source within 10 degrees from the driver's normal line of sight shall not be more than 1,000 times the minimum measured brightness in the driver's field of view, except that when the minimum measured brightness in the field of view is 10 foot-lamberts or less, the measured brightness of the light source in foot-lambert shall not exceed 500 plus 100 times the angle, in degrees, between the driver's line of sight and the light source.
The provisions of this section shall not apply to railroads as defined in Section 229 of the Public Utilities Code.

Prohibited Signs and Devices
www.dmv.ca.gov/pubs/vctop/d11/vc21467.htm
21467. Every prohibited sign, signal, device, or light is a public nuisance, and the Department of Transportation, members of the California Highway Patrol, and local authorities are hereby authorized and empowered without notice to remove the same, or cause the same to be removed, or the Director of Transportation, the commissioner, or local authorities may bring an action as provided by law to abate such nuisance.

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