This may be just a personal view, but I always thought that this sign meant No Cycling!
This is obviously not the case as cyclists in and around London and the South East seem to completely ignore it. I have even been almost run down by a cyclist whilst standing next to a sign just like this.
It is all age groups who seem oblivious to the sign as well. Older cyclists are just as bad as the younger ones and are often riding just as fast!
I believe this is one of the most pointless street signs in the UK as cyclists ignore it and no-one appears to enforce it. I am sure local authorities could save thousands by not bothering to put up a sign that is ignored by everyone!