More convinced it said SOC rather than 80c on that letter now.
0207 946
SOC 0221
My Theory:
SOC = Scene Of Crime
0221 = 2:21 Time of death
0207 946 Will give some form of identification of who the killer is or atleast narrow it down
Makes sense as why would Lauren assume the phone number is the number of the killer. Nothing suggests it unless there is more info like SOC, scene of crime.