Do I have to write my Handicap Index on my scorecard?

Yes, in South Africa. GolfRSA requires players to show their Handicap Index on the scorecard in handicap competitions. The Committee can also require you, in the Terms of the Competition, to write the colour course (tees) you played and your Course Handicap and/or Playing Handicap.

The Rules of Golf themselves (Rule 3.3b(4)) don't make you responsible for showing your handicap or adding up your scores. If you get the handicap or the addition wrong, there's no penalty under the Rules of Golf, because the Committee works out your handicap strokes and net score. What you are responsible for is the correct gross score on each hole.

Source: GolfRSA Rules of Handicapping 2024 club training (Scorecard information); Rules of Golf (2023), Rule 3.3b.