A countersignature is an additional signature that is required before a legal document is considered valid. Countersignatures are used to provide an additional level of control to arrangements that could potentially involve the loss of a large amount of money.
This additional signature is used to indicate that someone has verified the authenticity of the the primary signature placed on a document. The countersignature is used to indicate that the primary signer has indeed approved of the contents of the document and agrees to its provisions.
Countersignatures are required on many types of documents, and especially those involving the transfer of major assets, such as mortgages and money orders. They are also required on certain employment documents and insurance contracts.