Choose a simple format
A spreadsheet or plain text file is enough. What matters is consistency: one row or entry per observation.
Minimum fields
Record the date, the address, where you found it, what you checked and the result. Add a short note explaining anything unusual.
Never overwrite entries
When something changes, add a new entry instead of editing the old one. The history is the point of the log.
Review periodically
Once a month, scan the log for Omega Market addresses that have not been checked recently and mark them for review.