If your ex-employee has forged the experience letter and it is discovered at a later stage, you may issue an office circular stating that you have recently discovered a case of falsification of the experience letter with your company's details. Forgery is a criminal offense, and whoever does it is liable for legal action. The issuance of the circular is expected to create deterrence.
However, the issuance of the circular also has limitations. This is because conscientious employees will not engage in forgery. On the contrary, unscrupulous employees will remain undeterred and will seek out new ways to commit forgery.
Thanks,
Dinesh Divekar