Form I-420 shall be signed in duplicate and forwarded to the Headquarters Office of Inspections. After acceptance, each Regional Office of Inspections, the district office and the carrier will be furnished with one copy of the agreement. The transmittal letter to the Headquarters Office of Inspections shall indicate whether the signatory to the agreement is a subsidiary or affiliate of a line which has already signed a similar agreement. Correspondence regarding ancillary contracts for office space and other facilities to be furnished by transportation lines at Service stations in Canada shall be similarly handled.