The advertising underprints on the stamps of New Zealand are well known. Less well known are those of El Salvador.
Shown here are examples from the Bill Welch collection of the settings of nine on the 1894 Liberty issue.
These probably were created after Seebeck’s death in 1899 in an unsuccessful effort to market reprints to manufacturers in their wares.
The two settings of nine are on the 1c and 24c Liberty issue.
The single is on back of the 12c 1895 Arms issue with a specimen pen-line.
I have also seen examples on Nicaragua Seebecks but they seem to be much rarer than those from El Salvador are