- Spend your money on GPS locators for all your cabs.
- Have someone create an App for you that shows the location of all your cabs at the same time
- Give away the app to anyone who uses your cabs. (When they get in, ask them if they want your free cab locator app, make it accessible from the back seat of the cab)
- Put stickers on the separator window of the cab, invite Yelp Reviews (and all other user review sites) of your company.
You have hundreds of visitors willing to promote you every day... you just need to get the tool into their hands!
Just my .02