Airspace floor indicator picture

Quick answer：

An airspace floor indicator is a navigational aid used in aviation to display the altitude of the lowest safe altitude for aircraft to fly below. It is typically found in controlled airspace and helps pilots avoid flying into areas where they could potentially collide with terrain or other aircraft. The picture you mentioned likely depicts such an indicator, often in the form of a bright, contrasting color painted on the ground or mounted on structures within an airport or along airways.