Seals can be categorised into two main groups accordingly to their functionality:
1. Decorative and indicative seals
2. Security seals
Decorative seals do no need numbering, since their functionality is mainly that of dressing a box up and making it more appealing, while security seals absolutely need numbering to guarantee they are univocal and not replaceable.
Numbered seals can be manufactured in plastics, metal or as self-adhesive numbered labels.
To increase the security level of a seal, bar coding or data matrix printing on it is also recommended.
This kind of marking enables automatic identification techniques, thus minimising the human error introduced by operators.