Technically, fan-made items are illegal in the US 
without consent and permission by the licensed 
owners.  But many companies don't really care by 
wasting resources to deal with this small 
problem, unless someone is making a lot of money 
from those fan stuffs, then they may feel jealous 
and stop them.

My old friend used to have a fansite on Survivor 
that he made some money from the banner ads.  
Then CBS sent him a few letters, told him to stop 
the website.  Eventually, my friend did shut it 
down in case CBS is serious about suing him.