I'm not really sure why, but it appears the 1980s were a time of experimentation by banks trying to use Part 15 radio to communicate with drive-through customers. I am crazy about stories that describe practical applications. There is very little information available but here's what I've dug up so far...
Radio device transmits banks services from office to car
CTS Accounting Software Survey, September 25, 1983
Lee Cohen, chairman of Solar One in Virginia Beach, is the regional distributor of "Radio Realty," a low-power AM radio transmitter designed to broadcast repetitive, pre-recorded sales messages directly from a bank office to cars in line waiting for drive-in window service. Customers hear the broadcast by tuning their car radio to the frequency on the accompanying bank sign. Each radio transmitter costs $325.00
On the record: Ohioans tune to 'Broadcast Banker'
Bank Marketing, Washington D.C., December 1988
Society Bank NA (Dayton, OH) now broadcasts information on its products on AM radio to customers at the bank's drive-through windows. Signs at the branches tell drivers what frequency to tune to in order to receive "Broadcast Banker."
'Drive-up radio' entertains State Central CU members
Credit Union News. New York, November 17, 1988
State Central Credit Union (Milwaukee) has a Drive-Up Radio program to entertain and inform customers about its products and services as they wait in the drive-up teller line. The FM service is being tested for 60 days to judge customer response. A three-minute message is broadcast over a low-power signal that reaches only 300 to 500 feet. The message includes ways to facilitate drive-up service and it requests that members ask tellers for brochures to get more information on products or services.
Marketing news: radio game show entertains customers in line at drive-in bank line
Anonymous. Bank Marketing. Washington D.C., July 1986
Mount Clemens Bank (Mount Clemens, MI) has begun sending a 1/10th of a watt radio broadcast signal to cars waiting in line for drive-in banking services at one of its branches. The signal offers advertising and a trivia game. If the service is judged successful, the bank will expand it to other branches. About 400-600 cars per day use the South Branch's drive-in services.