You have served the community where you grew up, standing as its first line of defense against crime. You aren't a soldier, directing your gaze outward at possible enemies. Instead, your service to your hometown was to help police its populace, protecting the citizenry from lawbreakers and malefactors of every stripe.
While the Lamplighters were initially founded as a night watch that helped to install & maintain street lamps, it has since expanded to patroling the streets during daytime as well. The high amount ghosts & similar hauntings makes many members of the watch at least somewhat familar with curses, undead, & other paranormal activity.
Skill Proficiencies: Insight, & your choice of either Athletics, Investigation, or Perception
Tool Proficiencies: One of your choice
Languages: One of your choice
Equipment: A lamplighter uniform, which consists of a jacket, overcoat, & trousers of navy blue wool, a black top hat, black leather belt & boots, & brass collar insignia with your serial number. You also have a tin whistle with which to summon help, a hooded lantern, a flask of oil, a tinderbox, a set of manacles, & a pouch containing 5 gp.
You have spent some time in the local community on patrol & assisting with investigations. You are familiar with some of the stories of unsolved crimes, gruesome deaths, cursed lineages, haunted buildings, & other colorful local lore. You have advantage when making Intelligence (History) checks concerning local criminal & paranormal events. You also know where you can get information that is generally reliable on such matters. It can be a tavern with patrons eager to share horror stories, a local gossip with a taste for juicy scandals, a historian with centuries of records, or other fonts of exposition.
If you relocate to a new settlement or region during the course of your adventure, your character can spend their downtime to learn the lore of their new surroundings.
Use the tables for the soldier background in the Player's Handbook as the basis for your traits and motivations, modifying the entries when appropriate to suit your identity as a member of the city watch.
Your bond is likely associated with your fellow patrol members or the Lamplighter organization itself and almost certainly concerns your community. Your ideal probably involves the fostering of peace and safety.