Many college counselors and people who write recommendations are trained to write in a way that can convey the rank, if not with any precision. Many counselors will write that this student is “at the very top of the class” or “among the top students” to convey that the student in the top 10%. Weaker recommendations say something like, “she’s one of the better students,” which implies in the top 50%. I know that these words don’t help the middling or average student (although the absence of this language in your recommendation may itself be a message) but that’s how many schools address the lack of rank. Also, the school honor society or NHS may also be defined in the school profile provided to the college; it will usually say that the top X% of the junior class is selected, or it may give the number of inductees. So if you were selected for NHS, that’s usually a good indication that you are in the top 10%.