The bonds shall be issued on the full faith and credit of the Commission and the county guaranteeing the bonds. If the Commission decides to spend the proceeds of a bond issue throughout the metropolitan district, Montgomery County and Prince George’s County shall guarantee the payment of principal of and interest on the bonds. The following guarantee shall be stated on each bond: “The payment of interest when due and of the principal on maturity is guaranteed by Montgomery and Prince George’s counties, Maryland.”. The county executives of Montgomery County and Prince George’s County shall sign the endorsement by manual or facsimile signature on each bond. If there is any liability under the guarantee, each county’s liability shall be in the proportion the assessable basis for that part of the county in the metropolitan district bears to the assessable basis of the whole district. If the proceeds of a bond issue are to be expended only in or for the benefit of a portion of the metropolitan district that is in Montgomery County, Montgomery County shall guarantee the payment of principal of and interest on the bonds. The following guaranty shall be stated on each bond: “The payment of interest when due and of the principal on maturity is guaranteed by Montgomery County, Maryland.”. The County Executive of Montgomery County shall sign the endorsement by manual or facsimile signature on each bond. If the proceeds of a bond issue are to be expended only in or for the benefit of a portion of the metropolitan district that is in Prince George’s County, Prince George’s County shall guarantee the payment of principal of and interest on the bonds. The following guaranty shall be endorsed on each bond: “The payment of interest when due and of the principal on maturity is guaranteed by Prince George’s County, Maryland.”. The County Executive of Prince George’s County shall sign the endorsement by manual or facsimile signature on each bond.