There are several options/ideas before taking legal measures:
First, contact a towing company and arrange with them to put up signs warning that non-customers will be towed at the owner's expense. Assign one of your staff members to patrol the parking lot every half hour for the first two weeks, minimum, after the signs are posted. Even better, post someone in a security uniform for two weeks (minimum wage, but expensive). If your staff member sees someone park in the lot and not enter your business, have him or her immediately call the tow company. Word will get around.
Second, write a dated letter and distribute the letter to all the businesses in the area where customers may be close enough to use your lot. Be nice but firm. They're your neighbors. Ask them to please start informing their customers that all vehicles parked in your lot that are not your customers WILL be towed at the vehicle owner's expense. Drop off reminder letters every two weeks for the first month or two. (By the way, I suggest running off these letters or memos on brightly-colored paper, so that the other business owners are more likely to see them).
Now, using the above ideas (or any other type of improved signage, such as wall signs, painting "your business customers ONLY" on the spaces, etc., you should have no need for any legal remedies or cost.)
Here's another almost free idea. Have an employee meet customers at the door of your business and hand out parking passes for the dashboard, dated for that day. Again, this is just to help get word around that you're serious.
If you have one particularly problematic business neighbor, instead of just handing the owner "reminder" flyers, you may want to send a certified, return receipt letter (dated, signed, etc). This will cost you about $5.50. If you ever have to go to court, you now have an "exhibit" you can show the judge.
Here's another idea - if parking is really tough, contact a parking lot company about making your lot a paid parking lot. That way, you'll make extra money. Just a thought.
Now, if you have further questions, feel feel to ask follow-up questions. I'll be here all day, and there's no extra charge. I'm here to help you.
On the other hand, if I have answered your question to your satisfaction, please click on "accept" - otherwise, I won't be paid even a dime for my time.
By the way - just a thought - if you will be doing some new signage or painting, this is a good time to make sure that your disabled/handicapped parking is correctly marked and the right size. Again, just a thought - you didn't ask, I know. :)
My best to you,
Jane Doe Deer
Edited by Jane Doe Deer on 11/9/2010 at 7:38 PM EST