1. Identification: Signature is an identification method, which can confirm that the person who activates the mobile phone card is indeed a legitimate cardholder. This can prevent others from stealing or fraudulently using other people's mobile phone cards for activation.

2. Legal requirements: According to relevant laws and regulations, some communication operators need users to sign corresponding agreements or contracts when activating mobile phone cards and other services. Signature indicates that the user agrees to the terms and conditions and promises to abide by the relevant regulations. This not only protects the rights and interests of users, but also ensures the legal relationship between communication operators and users.