I didn’t want my background characters to have actual names (on the script) as to not confuse them with my main characters, so I label them with the simplest name and according to the reason why I use them.
For example, if I placed a character there to be part of a background scene for firefighters, I labeled them ‘Firefighter’. If there are more than one firefighter, I would either add genders (M, F etc.), numbers (1,2,3,4,5,6,7, etc.), or task (_______ Running, _______ Commanding, _______ Screaming etc.).
If your background characters do end up talking, even if it’s just a simple “hi!” or “bye…?”, please don’t have ‘BGCHARFEMALEDEMON3’ or whatever script name you chose as the display name. Give them an actual display name, or leave it blank, because it looks strange to the readers when they see that.
In addition, having the same background characters over and over in a script starts to stick out after a while and it isn’t realistic that you’d see the same people everywhere on a daily basis (unless your story setting was someplace with less people, then that’s reasonable.)