Vending machine stamps, known by different names alluding to the different machines and methods of production used have become extremely popular with the public at large. They are easily accessible by the public when stamps are required and the local post office is either closed or there is none close by.  Different denominations can be printed on the stamps at the time of purchase, different designs are used such as the XMAS stamps each year, the popular bird series, etc, they are self-adhesive and can also be purchased in small quantities. Many of the early ones are now extremely expensive because of the limited time an ATM machine may have been available at a certain place or certain time. Their popularity continues to grow.