an apparatus is disclosed for marking refillable containers , more especially plastic bottles , with code symbols for later ascertaining whether a container has to be refilled or separated . the part of the container in which is situated a manufacturer &# 39 ; s code present from the outset is photographed at a detection station by a camera . using code symbols applied previously as a reference marking , the place is determined at which a new code symbol of a round trip code is applied at a marking station with a laser . the number of such code symbols gives the number of fillings of the containers , and the data content of each code symbol contains a statement concerning the filling inserted in the container , the bottler etc ., in each case . with the aid of this , a certain filling sequence can be adhered to , for example , prevent a plastic bottle which previously contained a cola drink being filled with mineral water , whereas the reverse sequence would be permissible .