Debian Contribution Certification
If you are a DD and you'd like an official certification of that fact, you can ask the DPL to send it to you. It might be a nice addition to your resume.
Please remember that it takes anyhow some time to check the data and prepare one, so please refrain to ask one just for vanity; whereas if you need it for work or anything else: no problem, just go ahead and ask.
Alternatively, you can also confirm your status through the nm website, at https://nm.debian.org/person/loginname/certificate/, replacing 'loginname' with your DD username.
See example: example-certificate.pdf
Debian Project Leader
If you are DPL, you may use a LaTeX template created for that purpose. It's in the Git repository of the DPL salsa group.
Acknowledgements
Thanks to Agnieszka Cicha-Cisek (aga@prezu.one.pl) who designed the certificate template and Patryk Cisek.