This striking Bulgarian postage due issue shows a green 5 stotinki design with a bold black surcharge raising its value to 20 stotinki. Such overprints were applied during times of postal rate changes, allowing existing stocks to be reused efficiently. The stamp carries the official inscription “Доплащане” (Postage Due), marking its use for underpaid mail. These surcharges are of special interest to collectors of classic Bulgarian philately, as they highlight transitional postal practices. A fine example of early 20th-century overprint issues from Eastern Europe.