The certificate has more value if it is signed as in some contexts, the signature shows that the certificate is an official document.
For the time being, Youthpass certificates need to be printed for signature, as digital signature is not yet enabled in the Youthpass tool. Sometimes organisations send out the certificates by e-mail and ask the participants to print them out on their own. In this case the certificate would come without the original signature. If you prefer to have your certificate signed, please let your organisation know and ask for their support.