"The idea was to be a symbol." Trophy in LEGO Batman: Legacy of the Dark Knight

There are 50 Bat-Symbols on rooftops and in hidden corners of Gotham, and any 25 earn the trophy. They are the one collectible the radio towers do not mark. PowerPyx's Bat-Symbol guide has a screenshot of each of the 50. Collecting all 50 builds a T-Rex for the Batcave, which no trophy needs, and they do not count towards A Watchful Collector.