Free Traffic Legal Advice

There is an advance notice for a LH turn:-

and similar for a RH turn.

So one could consider the signage 'adequate'.

There may possibly be a 'technical' appeal based on Redbridge mismanagement of the enforcement process. This is usually their web pages for paying and appealing. Hippocrates may post to suggest something, so wait a while, but don't miss the pay/appeal deadline on the PCN. Such appeals are inevitably dealt with at London Tribunals with the full PCN penalty in play, but that is all, there are no additional costs whatever.

They have re-offered the discount, so it is now a matter of your attitude to risk. If you decide to take them to London Tribunals, the full PCN penalty will be in play; no discount. However, this is your maximum financial exposure, because there are no other costs whatsoever. If you win, you pay nothing, of course.

Having said that, I don't think your case is very strong, but see what the others say.