Yes
To be frank, I don't think the sign having red paint over the No Waiting symbol would win your case at London Tribunals. There is also the presence of the single yellow line, so the 'redded out' No Waiting symbol doesn't really mean you cannot work out what the restriction is. That sign says what the restriction hours and days are for that yellow line. Had the sign been seriously vandalised, you'd have a case, but here, no.
Of course, you have the absolute right in law to take them all the way to London Tribunals assuming you are the owner of the vehicle. The legislation makes the owner liable for PCNs not the driver.
Others may differ on my opinion, so wait a bit, but don't miss the deadline for the discount if you're minded to pay it, or the deadline for sending in reps or paying at the full rate.