 From 1840 to 1844 , the Penny Black , and other stamps issued , were obliterated with the Maltese Cross cancellation . There was no text or numeral to help identify any of these cancels as Irish , but some Maltese Crosses are uniquely identifiable with certain Irish towns , including Belfast , Eyrecourt , Cork , Hollymount , Limerick and Mullingar . From 1844 on , the cancels used included text or numerals that identified the post town . Cancels of both types are easier to identify if the stamp is still affixed to a cover , since this makes the complete postmark visible , but a stamp no longer affixed to a cover may still permit identification of the town of use if enough of the postmark can be seen on the stamp itself . 
