And which one would that be?
There's the M theme in Voluntary Retirement and Mother, the urban theme in Shanghai Drive and Adrenaline, the exotic motif in Komodo Dragon and Enjoying Death, Silva's ostinato in Someone Usually Dies and Deep Water, a signature bitonal chord progression (try and sustain and Em chord in your left hand, and play another Em chord on your right, followed by an F# chord) heard in Someone Usually Dies, Kill Them First, Breadcrumbs, and The Moors, Severine's theme heard in Severine; Modigliani and Komodo Dragon, plus the Adele theme.
Whether or not you find them memorable or hummable enough is up to you, but I'm fine with 'em.
I don't think the hummability of Newman's "themes" is at debate when compared to earlier films. It's no comparison. I don't think anyone in their right mind would put them on equal grounds. I don't think anyone watching this film would care about or remember for more than one day a freaking "Silva ostinato".
Thomas Newman singlehandedly (even with playing a bitonal motif with his other hand) delivered the most anonymous Bond score since License To Kill - which at least had some oomph - and in a series that is so closely tied to its musical identity, not to come up with a single theme that is able to stand on its own beside the Bond theme, in the 50th anniversary movie, is simply not acceptable.
Implying that some muddy "M theme" or that Requiem For a Dream motif fits that bill cannot be taken serious.
A piece like "Deep Water" could be placed in any movie, from Bourne over Thor to Planet Of The Apes.