Was this possibly an aircraft (Delta or another) using LAX Terminal 5? The protocol used by ground controllers when aircraft are being taxied between gates and hangars is to assign a call sign using the airport gate, with the word "tow" attached. Such as "United 68A tow" if Gate 68A is involved.
See this NTSB report summary where the issue arose:
https://www.ntsb.gov/ntsb/brief.asp?...14X41599&key=1