Legal Question in Real Estate Law in California

Re: Private Property on Government Land

You are allowed freedom of expression at your place of work. The Federal Government cannot make a rule prohibiting you from taking a stand on a political issue. However, it would be legal for your employer at your place of work to make an across the board policy stating that no one is allowed to put up posters of any sort in their vehicles when at the place of employment.

Re: Private Property on Government Land

The United States Supreme Court held, in Greer v. Spock (1976) 424 U.S. 828, that a military base is not a "public forum" and may be closed to First Amendment activities such as political speech and distribution of leaflets, if done even-handedly. The Court said that there was a strong public policy in favor of keeping miliary bases free of partisan political entanglements.

Since parking your car on the base is almost certainly a privilege and not a right, the base commander would not violate your Constitutional rights by banning your parking of a vehicle displaying electioneering signs.

So, I think it is likely you could be asked not to display the signs and a court would uphold the rule, but it is by no means certain that the navy would raise any objection in the first place, unless a policy is already in place.