Licensed opticians must wear name tags that show their name and license number.  They also must have their current license posted where you can see it.  

This way you know you're dealing with a licensed professional.  

Registered optician apprentices also wear name tags that clearly identify themselves as apprentices.  If you don't see a name tag and/or can't see a license, you have a right to ask for the credentials of the person who is measuring your eyes, adjusting your frames, fitting your contacts, and/or otherwise filling your prescription.