It looks like a document sent by a government. So instead of tossing it, I opened the mail. Just in case it is a notification of unpaid taxes or some kind of violation (not that I recall any...).
The first heading starts with "county participation." In the actual text, it says "our records indicate that your home at the above address may qualify for an Energy Cost Reduction. Incentives are available under the federal Energy Policy Act of 2005 and Section 25D and 48 of the Internal Revenue Code for homeowners who add solar energy systems to their homes."
"Federal Energy Policy Act." "Internal Revenue Code." Sounds like government related.
Well, it is a solicitation letter from SolarCity - the largest residential PV installer in the US.
At the very end of the letter, it also says "... local government are not associated or affiliated with SolarCity, and nothing herein is an express or implied endorsement by your utility or local government of SolarCity....
They got me. They made me open the letter and read it.