|This stamp was only issued with the first watermark, and I designate it as the 2p5c1E. Some specimens, like the one illuistrated below right, come with a "comb" perforation.
From the specimens and usages available, it is unclear to me which postal rates the issue of this stamp were intended for. The 2 1/2 Centavo is found on various philatelic covers. Here are quick links to
the "cents" section, the 2 1/2 centavo design page,
the 2 1/2 centavo issue page, the 2 1/2 centavo plate varieties page,
and the "cents" covers main page.