How can I tell if my grill pan is preseasoned?
Per the information on starfrit.com , there is no mention of the pan being pre-seasoned. But there is also no mention of needing to do so. 

From the maintenance tab on the linked page:


  Before you cook
  
  
  Remove all labels and packaging materials.
  Before using your new cookware, wash thoroughly in hot soapy water using a soft cloth or sponge. Dry completely.
  
  
  General cooking tips
  
  
  Prior to each use, it is recommended to add a teaspoon of cooking oil for better cooking results.
  
  
  Never heat an empty utensil. Be sure there is oil, butter, liquid or food before placing the cookware on the range
  or burner.
  It is not recommended to use high heat. Cooking on excessive heat can cause permanent damage to the surface and
  utensil.
  Never cut anything in the cookware or use utensils with sharp edges as to avoid damaging the surface.
  Add salt to water only after is has come to a boil. Salt grain deposit on the cookware bottom will attack the metal as
  the heat melts it down.
  
  


There is also other information about cleaning and oven use. 

All said, I don't follow a set rule about seasoning non-stick cookware even though I've often seen it recommended. But when I have heated oil in a non-stick pan it does seem to do better afterwards, especially with older pans. And I always hand wash non-stick cookware.

To sum up, I don't see how you could cause any harm by pre-seasoning the pan and occasionally reseasoning, even if it doesn't need it. But this is based on my experience and I haven't used this brand. 

The only other thing I can suggest is to contact the company and see what they say. Since they don't mention pre-seasoning, I suspect they will say it isn't necessary. If you do contact them, we'd be interested in what you find out.

And welcome to Seasoned Advice! 

EDIT:

I was assuming that the OP knew about seasoning a non-stick pan, as the question is about how to tell if a non-stick pan is pre-seasoned when new.

To be very clear, seasoning a non-stick pan is NOT the same thing as seasoning a cast iron or other bare metal pan. Should you (or anyone) decide to season a non-stick pan, please make sure to follow a recommended procedure.