 <unk> imposed by the Irish post office on mail bearing insufficient pre @-@ paid postage had the postage due collected by the use of these labels . Since 1925 there have been six series printed , with the design remaining the same until 1980 , though the colour and watermarks have changed . The Irish word <unk> , for penny , is used in both £ <unk> and decimal currency , but because it has the same meaning in each , the value on the label does not indicate whether the label was issued before or after decimalisation . Hence , identifying the issue of a label requires further information : if collectors knows the date of use , the existence of a watermark and if so which type , and the specific colour , identification will be easier . For example , the 3d value was blue between 1940 and 1969 , and stone colour from 1971 until 1980 ; it changed from a watermarked to a non @-@ watermark paper in 1978 . Additionally , the 1 , 5 and 8 pence values are seen in two different colours depending on the issue , while the 1 ⁄ 2d , 1d , 2d and 6d are seen with both watermark varieties . Except for the sixth issue , which has the word Éire in the design , there is no explicit country identity on any of the others . The first four series use only Irish words . 
