Sep-trial.slf

An ".slf" file extension can be associated with several types of files, but it's not a widely recognized format. Here are a few possibilities:

Do not attempt to open in a text editor – this can corrupt your terminal or lock your system. Instead: sep-trial.slf

with open('sep-trial.slf', 'rb') as f:
    data = f.read()
    if b'SEP' in data:
        print("Found SEP marker at offset", data.find(b'SEP'))

“Trial” strongly suggests: