I couldn't find an official logo on the official site, so I reused two images that appear to have been created for the event. They are somewhat strange, particularly the one on the right, but many things that emanate from Agon are strange.
A few days after I posted that, I leaned that the images were indeed designed for the match: Branding for the 2018 Match Unveiled (worldchess.com):-
Key visual for the 2018 World Chess Championship is controversial and trendy, just like the host city. [...] The 2018 key visual has been developed by Shuka Design and we are very happy to unveil it today.
The 'key visual', the image I had on the left of the '2018 London' post, appears in much larger format in the Worldchess 'Branding' announcement...
...The announcement also mentions,
As organizers of the match we've been busy for over a year working with artists and designers to develop a perfect key visual, the image that will be associated with the 2018 match and which will find its way onto mugs, posters, outdoor displays, venue design, media, broadcasting graphics and more.
As for the image I had on the right -- questioned by one source as Pawn-ographic? (rt.com; 'Chess world divided on "suggestive" Russian-designed logo for World Championships') -- it's already available on a poster: 2018 World Chess Championship 'Sexy' Limited Edition Print (worldchess.store). I imagine it will soon be available on mugs as well.