There is a special column that is called סימן which is meant to use for such a thing. It comes up in most places already and can be added to other places as well.
The current search option searches this column too. So to look for the account below you need to search for טייט,יוא,נחום,בלום. The first is part of the last name, the second is part of the first name, 3rd and 4th are anything including this column. You can include any text there. It's not included in any mailing for the person, it's just a סימן for you.