What callsign should an ultralight use? I plan to operate an ultralight aircraft domestically (in Oregon, USA) in uncontrolled airspace and will not venture out of the country nor will I come near the Canadian or Mexican borders.

I have searched a bit and found that as long as I'm going to be operating domestically, I don't need an FCC license, however in AC 103-6 it states


  c. Traffic Advisory Practices at Uncontrolled Airports.
  
  In all radio communications, ultralight operators should state the word 
  "ultralight" followed by the call letters assigned by the F.C.C. on your 
  radio license, i.e., "Ultralight 12593U".


How can I use FCC call-letters if a license is not required domestically?  Since ultralights aren't required to be registered, I won't have a tail number to use either.  Do I just make something up like "ultralight whisky bravo" (my initials)? I do have an amateur radio license, but I'm guessing that isn't relevant here.
One of the suggested communication strategies for uncontrolled airports is to announce the type of aircraft and color. e.g. “Brown and white Cherokee entering downwind”. 

Rather than using your initials, which like the tail number, don‘t really give any information, why not use your color or some distinguishing feature. e.g “Red tricycle ultralight” or “Blue weight-shift ultralight”. 

Anyone out there would have a better chance of knowing what to look for and seeing and avoiding you.