Doylestown police Chief James Donnelly tells The Intelligencer that the drawings didn't break the law.
He said Thursday that the images have to be "indelible and financially costly to remove."
Police had issued citations to 18-year-old Connor Logan and a 17-year-old friend earlier this month for drawing a whale and sea turtles on a street downtown.
Logan has said he found the chalk in a parking lot and thought the drawings were "harmless."
Donnelly said last week that police filed charges because it was an attempt at vandalism. He also said the doodles might link the teens to chalk graffiti on local businesses and buildings.