Use the adjective glanceable to describe something that can be understood instantly, with a quick look. Road signs are designed to be glanceable, so drivers don't waste time wondering whether they're supposed to come to a full stop.
Glanceable is very much a 21st-century word that's mostly used for describing images or information on an electronic screen. Mobile phone apps are constantly evolving to be more glanceable — so that users can read text at a single glance, or almost instantly understand map directions. Anything that can be used this way, from the scoreboard at the football stadium to the weather forecast on your fancy electronic watch, is glanceable.