Don't let him take it down.
cite this supreme court case ruling:
City of Ladue v. Gilleo (1994)
"“Displaying a sign from one’s own residence often carries a message quite distinct from placing the sign someplace else, or conveying the same text or picture by other means. … Residential signs are an unusually cheap and convenient form of communication. Especially for persons of modest means or limited mobility, a yard or window sign may have no practical substitute. … Even for the affluent, the added costs in money or time of taking out a newspaper advertisement, handing out leaflets on the street, or standing in front of one’s house with a handheld sign may make the difference between participating and not participating in some public debate.”
http://www.firstamendmentcenter.org/faclibrary/case.aspx?case=Ladue_v_Gilleo
Lower courts refer to this when they strike down petty city ordinances.
See - Curry v. Prince George’s County (1999) ( federal court in Maryland) - They struck down a time limit of 45 days for political signs.
“There is no distinction to be made between the political campaign signs in the present case and the ‘cause’ sign in City of Ladue,” the court wrote. “When political campaign signs are posted on private residences, they merit the same special solicitude and protection established for cause signs in City of Ladue.”
Arlington County Republican Committee v. Arlington County (1993)
Eliminated a two sign limit.
“the two-sign limit infringes on this speech by preventing homeowners from expressing support for more than two candidates when there are numerous contested elections.”
Supreme Court of Ohio ruled in City of Painesville Building Department v. Dworken & Bernstein Co. (2000)
Had this to say about mandatory removal of signs in certain period of time:
“Although the Supreme Court has not considered the issue, the overwhelming majority of courts that have reviewed sign ordinances imposing durational limits for temporary political signs tied to a specific election date have found them to be unconstitutional,”
As long as the sign is not breaking some small rule like distance from road or size he is protected via 1st Amendment.