Indication of Current Status in the U.S.
Form I-94 receipt(Arrival/Departure Record) verifies a lawful admission to the U.S. in a specific status and any defined expiration of that status in the U.S. When a nonimmigrant is admitted to the U.S. he or she receives a stamping inside his or her passport. The stamping of the passport must correlate with the intended visa status and duration of lawful presence.
Expiration of Legal Status
For many types of nonimmigrant visa classifications the passport is stamped with a defined expiration. Foreign nationals with defined expirations of status must depart the U.S. or extend or change their status before the expiration is reached.
Nonimmigrant visa classifications including F and J should indicate the recognized and proper visa status as well as "D/S" which stands for "Duration of Status". A passport stamped D/S does not indicate a date-defined expiration date, and therefore the indicated status remains valid provided that all conditions of lawful status in the U.S. are met.
See SEVP's webpage on Duration of Status
Changes of Status
When an application to change or extend nonimmigrant status is approved, the USCIS will issue Form I-797 containing an I-94 coupon (in the lower-right of the form) which should be torn off and stapled into the applicant's passport as would an I-94 card received when admitted to the U.S.
Verification of Status
You will still need to ascertain that the correct information has been entered by Immigration at the port of entry, and you have therefore been admitted to the U.S. under the proper status. To retrieve I-94 data, as well as the ability to print an I-94 facsimile for applications and benefits, please visit www.cbp.gov/I94.