WKYC-TV Channel 3, Cleveland
Sign-Off from 1976

As far as I'm aware, this may be the oldest existing home video recording of a U.S. TV station signing off in circulation. It was in 1976 that the videocassette recorder (VCR) made its debut here in the U.S.. The clip begins with the closing graphic of the sermonette, Credo. The sign-off announcement follows, delivered by longtime station announcer Jay Miltner (now deceased). This clip also features a late-1970s variation of the NAB's Seal of Good Practice. At the time of this recording, the NBC network owned WKYC-TV. It is currently owned by Gannett. You can view WKYC-TV's colorful history on this Wikipedia entry.

WHIO-TV Channel 7, Dayton OH
Sign-Off from Summer 1978

An ancient sign-off from the Miami Valley's longtime CBS affiliate station. It is preceded by several minutes of the weather report from the encore presentation of that night's 11 o'clock news. The sign-off also makes mention of its sister AM and FM radio stations, in which viewers are invited to tune in to. My apologies for the quality of the clip, for it was encoded from a RealMedia file that was posted on Dave Reilly's old TVDX Detriot site.

WUAB-TV 43, Lorain/Cleveland
Sign-Off from 1981

A plain TV sign-off, slowly articulated by announcer Marty Sullivan and features a graphic consisting of housetops with TV antennas atop them. It is preceded by a U.S. Marine Corps SSB film featuring the Iwo Jima Memorial in Washington, D.C.. WUAB was originally owned by United Artists Broadcasting (hence the call letters), who sold the station to Gaylord Broadcasting by the time this clip was recorded. It is now owned by Raycom and is affiliated with MyNetworkTV.

WCLQ-TV 61 (now WQHS), Cleveland Sign-Off from 1982

Not a TV sign-off in the traditional sense, but an announcement to close out its day of free programming leading into its Preview subscription programming (which the station would drop in 1983). Following this is a scrambled signal test leading to a Preview telecast of the Cooney-Holmes boxing match from Las Vegas. From 1986 to 2002 this station ran Home Shopping Network programming. The Univision Hispanic network bought the station in 2002 and operates it to the present day.

WTVN-TV 6 (now WSYX), Columbus OH Sign-Off
from 1986 or 1987

The exact year of this clip is uncertain. It has to date before August 1987 when the station's ownership changed and the current call letters were adopted. This slickly-made sign-off features numerous views of Columbus at night and various cultural and recreational happenings. It ends with the SSB performed by the Columbus Symphony Orchestra with some superimposed fireworks thrown in at the end for good measure!