Can I add the Salesforce Certification logo to my business card?
Are you permitted to add the Salesforce Certified Professional logo to your business card?
Check this Guide to Certification link.
It States that you can use the Salesforce Certification logo on Business cards. Check point #2.
When you earn your credential by passing the requisite certification exam, you get:
A Salesforce.com Certified certificate
A Salesforce.com Certified logo to use on business cards, resumes, email signatures and social networking profiles
Free access to Release Training materials
Membership in the exclusive Salesforce Certified Professionals community
Personal growth and professional advancement
The link is last UPDATED July 2014. I will update this answer if I find any updated link