I hadn't heard of it until it appeared on here!
Have googled it a little, and here's my take on it:
A French comedian used the gesture in what has deemed to be an anti-semitic comedy routine. Under French Law, this comedian has been arrested, and charged for that offence.
Nik Anelka is a friend of the comedian, and apparently used this gesture as a symbol of support for his friend back in France.
It appears that the gesture was pretty much unknown until this comedian used it, some claim he invented it, and it has kind of become a trademark for him.
So, in judging whether Anelka's gesture was offensive or not, I do think we need to take into account the society and racial situation of the country from whence it came. The law in France, indeed the attitude toward racism, sexism, religous bigotry et al is very different to the UK.
The head of one of the biggest Jewish organisations in France has said that it wasn't offensive I think the FA should take note, because it is a FRENCH organisation, and not the opinion of an English 'advisor'.
I don't know if there is more history to the gesture than I have found, but I think we need to be careful of not going too far with what is deemed 'offensive'.
So, when refereeing I will stick to the old work-place adage that if the person it is aimed at finds it offensive, then it must be.
Question from me then - who was Anelka aiming the gesture at?
As a PS:
We have a youth referee here, and a couple of older ones, who, when using 'straight-arm' signals use a flat hand, palm down. So indicating a GK, direction of free kick etc. I have pointed out to them that every time they give a corner, they are doing a Nazi salute, but here, that isn't a problem. In the UK, I am sure there would be some comment from some smart-arse that would/could undermine the ref, or even claim to be offended by it.
Different societies, different histories, different standards and cross-judgement can get very tricky.