First of all we should know what profession means to think about engineering as a profession.Profession is a occupation in which a specialized knowledge about a subject,science or a field is applied.It is generally applied to vacations that include prolong academic training and a formal qualification.
Engineering is a specialized techniqual occupation especially in nineteenth century after it became more narrowly on applying mathematics and science.
Also if we look at the definiton of engineering we can see that,"engineering is the discipline and profession of appliying scientific knowledge ..." .
We can also classify the engineers as Professional Engineer,Chartered Engineer and Incorporated Engineer.
Briefly,Professional Engineers are the licensed engineers and we can say from here engineering is called a profession tells us it is also a licensed occupation.