1. Let's go with the obvious. The Merry Christmas legend isn't dressed up in the swirly-whirly font that usually festoons this sort of thing. It's all a bit redolent of far left newspaper fonts (specifically the Weekly Worker), an italicised - playful - version of the distinctly humourless, revolutionary headlines past and present. It could be read as a polite reminder that Jeremy's politics remain and won't be a-changin'.
2. The snow has multiple meanings:
a) What kind of cyclist leaves their bike out in the snow? One, I would suggest, who didn't know the white stuff was about to hit. Up until the tax credit debacle Jez was doing alright, but the backlash Harriet's instruction to abstain on the vote generated fired the boosters underneath Jeremy's campaign and won him the leadership. The snow here is suggestive of the surprise situation Jeremy finds himself in, of a man unprepared for the political weather.
b) We know the bike is Jeremy's favoured method of transport. We know that his leadership so far hasn't proven the smoothest of rides either, and yet he ploughs on. A bike covered in snow not only shows that Jeremy is aware of his journey's difficulties, by popping it on his card he's advertising his awareness.
c) The snow covers a quintessentially British scene, much like the blanket of radicalism now settling upon the old Westminster consensus.
3. Bicycles have a special place in the official narrative of the Chinese civil war/revolution. That these bikes are in deep freeze could be saying there will definitely be no more Chairman Mao gaffes.
4. You'll notice there are three or four bicycles in the scene, and they're probably not going anywhere. In other words, and unfortunately for rebellious-minded MPs, Jeremy and his team are not getting on their bikes. They're sticking around and won't be shifted. Merry Jezmas!