- Amplification and PA
- No speaker stacks at all means you are before the mid-1960s. Column speakers flanking a stage put you in the 60s; wall-of-sound rigs and delay towers are 1970s and later; line arrays hanging in curved chains are late 1990s onward.
- Stage lighting
- Footlights and chandeliers say concert hall or music hall. Par cans on scaffold trusses arrive in the 1970s, moving heads in the mid-1980s, and LED walls behind the band after 2005.
- Instruments
- Harpsichord, natural horns and gut strings point pre-1800. Solid-body electric guitars start in the 1950s, synthesisers become stage furniture in the late 1970s, and laptops and controllers after 2000.
- The crowd
- Seated rows in formal dress read as a concert hall or an early bandstand. Standing fields, tents and mud say a post-1969 festival. A forest of raised phone screens is 2010 or later.
- The room itself
- Horseshoe balconies and boxes place an opera house; a gilded shoebox hall reads as central European; a converted warehouse or a stadium bowl narrows both the country and the era of the building boom that produced it.