First and foremost, welcome to the forum and I applaud your ambition to go mobile and enjoy this obsession we call detailing as a full-time job!
As most will tell you, the most effective and cheapest (actually, it's free) form of advertisement is word of mouth. You mentioned doing a few details daily. Those customers will more than likely get your name out when somebody talks to them about cars. If you don't get more customers this way, you could offer some sort of referral incentive, like a 50% off a service or even a free service for everyone who brings you a new customer.
You can also try a more assertive approach by just walking up to someone's house with a dirty car in the driveway and giving them the lowdown on what a quality detail is and why their car needs it. Mind you, this method works most effectively in wealthy neighborhoods

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Flyers have proven to be effective only in some areas at certain times. In my case, for example, I live on the main street of my neighborhood, and everyone driving by sees me when I'm detailing a car. There have been some people who became interested in my services when they saw me working. Every one of those people have since bought a detail and are regular customers now. I figured, hey, why don't I stuff some mailboxes with flyers? Then all those curious passers by can get some contact info and see what services I offer. Well, I've received 5 phone calls and counting since Friday (when I distributed flyers). This is a flyer success story. However, going to the mall and putting flyers under windshield wipers will most definitely not work and will waste the money you spent on the flyers.
Back to the referral thing, you should keep a stack of business cards handy. Word of mouth and business cards are a match made in heaven when it comes to marketing your business. Someone will ask for a card most of the time if they have someone in mind who could use your services. You wouldn't want to be in that situation without cards. Another good thing to have on hand is brochures. A professional-looking, all-inclusive trifold is impressive. Just hand the customer one of those and a business card. I assure you, they will find their way to another potential customer.
Another great way to get your name out is having vinyl decals made for your rig. Mobile guys like 1CleanWS6 and Clean Dean have done this, and I'm sure it's helped them. You can be as simple as "Your business name, auto detailing, phone number, e-mail address" or a fancy logo with gradient text and all sorts of info. While on the subject of this, you could have some polo shirts, hats, t-shirts, or detailing aprons with your logo on them. Wear the stuff when you're detailing, and you'll get more attention than if you're wearing a white t-shirt and blue jeans.
That's about all I can think of. If there's more, someone else will chime in.
Good luck with your business!