The sign you have posted is the sign for the yellow line you parked on. So on the face of it, being parked on 16th April, a Tuesday, you were in contravention, hence the PCN.
When you parked on the yellow line, did you look for the controlling sign ? Also what was the purpose for parking there, as there are two exemptions to yellow lines ?
Please also post the back of the PCN, so we can check it for fatal errors of content.
PS: Never, ever, assume anything about parking in London. Streets are patrolled 24x7 and councils make £millions from PCN penalties.