The aim of the discussion is to determine the place of biometric electronic signatures (the so-called dynamic signature, or in short – biometric signature) within the general structure of electronic signatures under the eIDAS Regulation and to indicate whether the processing of personal data from dynamic signatures will in all cases be subject to the restrictions of Article 9(1) of the General Data Protection Regulation (GDPR). The lack of a legal definition of a dynamic signature, its technical nature and specific formula, combined with the characteristics of biometric data under the GDPR, raise significant interpretative doubts. The problem mainly concerns the classification of personal data processed (collected) when creating a digital version of a handwritten signature. The analysis leads to the conclusion that not every use of a dynamic signature involves the processing of biometric data within the meaning of the GDPR. Signature data will be treated as biometric only in specific situations where it is processed using special techniques for the purpose of identifying or authenticating a natural person. The authors thus point to the need for the controller to assess the context of personal data processing on a case-by-case basis, as it is the purpose and manner of use of the technology that determines whether dynamic signature data qualifies as biometric data within the meaning of the GDPR.