¿could be Divorced/Single?
Hope this helps

D/S stands for duty station.

Duty station is the city, town, country or State where an employee works or where his activities are based.

The Duty Station Locator System is intended to facilitate the Federal civilian personnel community's ability to locate duty station names and codes for use in processing personnel actions and reporting workforce information to the Central Personnel Data Filed (CPDF).

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It refers to the period of time during which a visa is valid, and therefore it represents the period the person can remain in the country. I think it may be there in case one of the future spouses is not English.

Here are some references and examples:

http://www.paulhastings.com/publicationDetail.aspx?publicati...
The DHS rule seeks to alleviate this problem by automatically extending until October 1 of the following fiscal year the duration of status and employment authorization of any F-1 student who is the beneficiary of a pending H-1B petition and a request for change of status.

http://www.resideenusa.com/content/view/801/81/
Los estudiantes F-1 serán admitidos y se les expedirá tarjeta de entrada/salida I-94, con la notificación “D/S”. Esto significa “Duración del Status”, o hasta que ellos completen los requerimientos que piden los programas educacionales...

Hope it helps!