Threat, Duress, Coercion (TDC)
"TDC" is an acronym used by the anti-government sovereign citizen movement to refer to "threat/duress/coercion." Some soveriegn citizens put this acronym next to a signature (or, in some cases, a zip code on an address) to indicate that they are not signing voluntarily, and that their signature is invalid and does not constitute a contract with the government that would force them to surrender their sovereignty. It dates back to at least 1992.