In my catalog this looks most like either a Scott 319 Perforated year 1903
or a Scott 320 year 1906 Imperforate. But it is neither. also both are listed as carmine and yours looks rose. I can't imagine how your stamp happened. It seems odd.That is not a lot to tell you of course. I wondered if a vertical imperforate coil had been trimmed off the coil by someone to avoid tearing. But I could not find such a stamp. I think it is interesting and worth the looking into. By all means save it.