Method and device (10) for marking objects (100), particularly for marking objects in banknote cassettes (1) or in other valuable object storage spaces. There is used a container (60) which can be punctured or otherwise opened and which is placed adjacent the object/objects (100) to be marked. The device includes means (13) which is caused to puncture or otherwise open the container (60) when necessary, so as to enable the content (61) of the container to come into contact with the object/objects (100) and therewith mark said object/objects and/or render the same useless. The marking device (10) and the container (60) fitted thereto are placed in the upper region of the space (1) so that the container is able to come into contact with said object/objects (100) at least partially with the aid of gravity. The puncturing means/opening means (13) is released from an active rest position when an alarm is triggered, so as to slit or otherwise open the container (60) in a guillotine fashion.