If there is one qualification that seems to be required of anyone wanting to run as London mayor it is the instant recognition factor. Even better if they can dispense with a second name and simply be known by their "showbiz" billing.
Just ask Madonna, Brad, Arnie or Ed (perhaps not the last one, he was a talking horse) about the power of a brand name.
So Boris and Ken had an immediate advantage over others who have fancied the job over the years, including Frank (Dobson), Brian (Paddick), Jenny (Jones) and even Steven (Norris who, unfortunately for him, was widely and unhelpfully known for his unprintable nickname which referred to his string of extramarital affairs).
A single-word brand is the clearest possible sign that you have arrived. It suggests there is not another person on the planet with the same name - or at least no one anyone cares about.
It is also great for the wider product branding that accompanies the mayoral race. It is short, catchy and above all else, familiar. Livingstone and Johnson alienate where Ken and Boris embrace - well Boris certainly embraced anyway.
So what chance Diane Abbott, whose public utterances and tweets since her sacking from the Labour frontbench last week have only served to encourage the view in Westminster that she is set on putting herself forward for the Labour nomination for the 2016 contest?
Actually, pretty good probably. She may not be known as Diane or even Abbott or some BoJo-style label (DiBo perhaps!).
But she does have a degree of recognition way ahead of any of the other suggested contenders - David Lammy, Sadiq Khan, Andrew Adonis et al. She shared, and will start sharing again, a TV couch with former Tory minister Michael Portillo and there will be no surprise if she turns up on all sorts of other TV platforms in the coming months.
What about Eddie
The one possible exception is Eddie Izzard, who has openly declared an interest in the job. He is a friend of Labour but his most recent remarks suggest he is not thinking about the 2016 campaign.
But there is pretty strong opposition against him in the Labour ranks, with one former minister telling IBTimes UK: "The last thing we want in City Hall is a comedian - at least, not another one."
That uncharitable view, of both Izzard and Boris, actually goes to the nub of the problem. London Mayor is a celebrity job and you need to have that X Factor before you stand a chance of winning a party nomination, let alone the election.
Abbott would undoubtedly not be the Labour leadership's preferred choice and, should she throw her hat into the ring, Ed Miliband would probably want to cast around to find a suitable candidate who could be guaranteed to beat her.
The fact the party is toying with the idea of holding US-style open primaries to select their candidate only hints towards the celebrity factor plot and could help Abbott. She may have her "issues", being a declared left-winger who sent her son to a private school, for example but could the recognition factor trump that?
The last thing Labour would want would be a re-run of the embarrassing and unseemly attempt to stop Ken Livingstone in 2000 by "persuading" popular London MP Frank Dobson to stand against him.
The upshot of that unhappy affair was that Frank lost credibility, Ken quit and stood as an independent and then went on to win. Labour have since admitted it was all very badly handled so they won't want to go there again.
But that does not rule out the strong possibility that party managers will attempt to persuade a strong, well-known and credible candidate to stand so long as he or she can stop Abbott in her as-yet-undeclared tracks.
Step forward former postie, Chancellor and Home Secretary, the effective and popular Alan Johnson?
Well, maybe not. He has shown diminishing interest in catapulting himself back into the front line and it would be another huge mistake for Labour to have a conscript rather than a volunteer.
So it could yet be DiBo. The trouble with all this, of course, is knowing whether Abbott's recognition factor means Londoners actually like her.
And ultimately, that is the one factor that is probably even more important than celebrity - likeability.