"Eastercon" is a registered trademark and full details of the ownership, use etc. are shown at
Most of the rest of this article is based on that webpage.
Rules for using the Eastercon trademark
As it says on the above website
Does a convention or a bid need written permission?
In practice, getting permission tends to be a verbal conversation on the lines of: "May we?" "Yes". There's no official contract, and very few terms and conditions.
What are the terms and conditions?
One of the convention's publications must state that:
"Eastercon is a registered trade mark and is used with permission"
Whoever's in charge of publications gets to pick which one. That's it, as far as the trademark holder is concerned.
Do people writing about Eastercons, or thinking of running one, have to get permission to use the trademark?
No. That would be very officious and bureaucratic.