Using little numbers like that is usually them (like all NYPD) truncating their 10-codes because saying "ten-[number]" takes a whole ton of airtime by their standards and they'd rather say it short and suffer the occasional confusing moment than soak up an extra half second. '10-75 directed' is a directed patrol, very simply. Not necessarily used solely by ESU (could presumably be used by any patrol officer who for instance is checking on a location mentioned for attention in roll call), but that's just where you've happened to hear it.