What type of radio navigation aid provides audio for station identification?

The Automatic Direction Finder (ADF) is a radio navigation aid that provides audio signals for station identification. This functionality is crucial for pilots as it helps them recognize the specific navigation aid they are receiving signals from. The ADF works by receiving signals from Non-Direction Beacons (NDBs), and when tuned to an ADF station, it emits a Morse code identifier that can be heard through the aircraft's audio system. This allows crews to confirm that they are indeed aligned with the intended navigation aid.

In contrast, other options do not provide audio for station identification. The Global Positioning System (GPS) primarily relies on satellite signals for positioning and does not include an audio identification feature in its basic operation. Marker Beacons inform pilots of specific positions along an instrument approach but usually do not provide identifying audio; instead, they serve as visual and tactile alerts when overflown. The Aircraft VHF Navigation System functions using VHF radio signals to determine location but lacks an audio output for identification purposes. Thus, the ADF stands out as the correct answer due to its specific functionality in providing audio station identification.