You can freely use Scrum Level resources for analysis, assessment and agility improvement activities of your own team or company, as well as the Scrum Level brand to refer to them in any field.
 

You can apply for a professional license in the Scrum Manager member area ("Professional Area" > "License") to use Scrum Level resources for professional consulting activities, as well as for the use of the Scrum Level brand to refer to them in any domain.

Both of these include conducting independent Scrum Level assessments. 

If you require the assessment to be an official, not independent, Scrum Level-issued assessment, it must be performed by a certified assessor.
 

From the "Professional Area" > "Refering companies" as described on the question: How can I put in the directory of commited companies the improvement actions carried out in my company or in those of my clients?