Ionics vigorously defend unauthorised use of there trademark logo. If you have one of their systems then they will supply you with the details for you to get it put on your vehicle.
Design your own...try not to look at the Ionics one, take your time, look at others that are about for inspiration.
The idea is to try and be unique, but be careful you don't go over the top!
Those that look at your van need to know what you do and how to contact you, fancy artwork can detract from that message if you aren't careful.
Ian