Betula, it would have been more helpful if you had provided us with additional information about your requirements. I see that each of us has interpreted it differently!
Interpreting Your Requirement
Let me first interpret your requirement. As per the company's policy, HR needs to document whether an employee is single or married. You want to send an email/memo/circular to the employees, asking them to inform HR of any changes in their marital status.
If this is the case, you may consider stating: "As per the company's policy, HR needs to document whether an employee is single or married. Please refer to the policy document for details. Kindly inform HR in case of any changes in marital status for documentation purposes."
Now that you have received numerous replies, it would be good if you respond.
Cheers!