The sign, which was up for about 15 minutes outside the Belton restaurant Sunday, called on the chiefs to "scalp" the Washington Redskins, as well as "feed them whiskey" and send them "2 reservation," the Kansas City Star reported Monday.
"It was inexcusable, offensive and wrong," a Sonic manager said.
The manager said the sign was only up for about 15 minutes, but in that time it was photographed and posted to several websites.
The restaurant did not say who was responsible for the sign or whether disciplinary action would be taken.
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