El Salvador Post-Stamps
"1867 stamps belong to the first issue of Salvadoran stamps ever.
1889 stamps circulated the black overprinted bar on top only.
The bar was used to hide the legend on top: UNION POSTAL DEL SALVADOR. The country's post office was officially called other way: CORREOS DEL SALVADOR, so the error had to be corrected before the stamps were made available for sale." - Filatelia Cuscatleca
