usually if you go to the hospital and are of the age to mentruate they will ask when you have had your last period. If it is an emergrncy then they will soon discover the little string and know. Believe me as a nurse it is no different for us to "check" these things out as it would be for a mechanic to check the oil ina car... all matter of fact.
I used to work at a general hospital. We were so used to seeing naked bodies that we said that if every patienty got out of bed and walked single file down the hall naked we would just wonder where they were going.!