Step 1: Understand the topic.
The question is about High Security Registration Plates (HSRP) for vehicles under the Motor Vehicles Act, 1988 and its rules. These special plates help stop number-plate fraud and make vehicles easier to identify.
Step 2: Who made the rule.
The Ministry of Road Transport and Highways amended the Central Motor Vehicles Rules to make HSRP compulsory. The key point is the date from which it became mandatory for all new vehicles.
Step 3: Recall the cut-off.
The rule made pre-fitment of HSRP compulsory for all new vehicles manufactured on or after 1 April 2019. So the year the mandate came into effect is 2019.
Step 4: Why the change was made.
The aim was uniformity across the country and better security, since these tamper-resistant plates support easier tracking and identification of vehicles.
Step 5: Rule out other years.
2018, 2023, and 2024 are not the year the all-new-vehicle pre-fitment mandate started. The correct cut-off is the 2019 notification.
Step 6: Final answer.
The mandatory pre-fitment of HSRP for all new vehicles came into effect in 2019.
\[ \boxed{\text{2019}} \]