First off, the 1st amendment does NOT protect "commercial" speech.
More to the point, I find those signs irritating enough that I’ve done some research on the situation in the past. Political signs, as opposed to advertising signs, are apparently allowed ("Permitted"). In fact, most, if not all, Virginia counties make it a crime to remove them. In my opinion, that's not right, but it's what we got. The problem devolves to the cleanup afterward...
The operative laws on highway signage are strewn through the Va. Code all over the place, so it would probably take a really smart person to devolve them all into one coherent story, but the snippet of code at:
http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+33.1-373, provides two important clauses:
1. “... Advertisements placed within the limits of the highway are hereby declared a public and private nuisance and may be forthwith removed, obliterated, or abated by the Commissioner of Highways or his representatives without notice ....” This refers solely to unpermitted signs (see 33.1-355), of course.
2. ... “When no one is observed erecting, painting, printing, placing, putting, or affixing such sign or advertisement, the person, firm or corporation being advertised shall be presumed to have placed the sign or advertisement and shall be punished accordingly ....”
Now, skip over to:
http://www.virginiadot.org/programs/prog-aah-faqs.asp, and note that if one adopts a highway, “As an Adopt-a-Highway volunteer, you are considered a representative of VDOT, with the full backing of the agency’s commissioner.”
Ergo, in theory, one simply has to apply to, and be accepted by, Adopt-a-Highway, after which one can spend two years removing all the unpermitted signs one wants to (probably including within many neighborhoods -- refer to 33.1-353 and 33.1-36), and, if they are aggressive, they can push the DMV to prosecute the sign purveyors to the tune of $100 a sign.
This also points to a slight quandary vis-a-vis Pat Herrity’s commment wherein he says, “Under the current Virginia Code, a County does not have the legal authority to remove signs from VDOT rights-of-way unless it enters into an agreement with the Commonwealth Transportation Commissioner authorizing it to do so.” Yes, but that conflicts with the other -- would that make the rule County-No, Individual-Yes?
If the legislators really want to take an interesting step in getting some incentivized help with this blight of signs, they might consider modifying the code to give the “VDOT Representative” removing the sign (or, alternatively, any person reporting an offending sign) $10 of the $100 fine thereafter collected. That might even provide an added incentive to attract more volunteers to the Adopt-a-Highway program.
Ah yes, I can see it now -- the Commonwealth-Incentivized Sign Policing and Investigative Group (CISPIG)...