Sounds like a good opportunity to sell a logo. Here is a scenario that happens at our shop.
Customer: "I need you to put this design on a sign."
Us: "Did the designer who created this supply you with a vector version of that art. Perhaps he or she put it on a disk for you."
Customer: "No I don't have a disk or any files."
Us: "OK then. We have 4 options moving forward.
1. We could trace this design assuming you are the owner of the design, but it takes time to do that and we would charge for that time.
2. You could ask the original designer to supply you with a vector file, this way we won't have to trace it, thus saving you money.
3. Usually it's easier for us to design something from scratch compared to tracing a design, tracking down the exact same fonts, etc... We can design something new and it will look and work better than what you have there anyway.
4. Or we could take the opportunity to create a brand new logo for you. The benefits of creating this logo is that we would be creating something that would work on all sorts of different applications, not just this one sign. After creating something you like and that your customers will respond well too, we will supply you with a disk filled with your logo in multiple formats. This way, when you go to get signs made, t-shirts made, business cards, etc... you wont be charged every time someone has to recreate or trace your new logo, because those files they need will be on that disk. This is the only option where we will provide you with art files in multiple formats. You would have to buy a logo from us, to use any design as a logo."
Possible Customer Response: "Yeah but I've been using this (old) design for years, it's my logo I think I might rather have you trace it."
Us: "We can certainly do that, however, consider this. Companies update their logo and image all the time, even the really big, successful ones. In fact they do it all the time because they realize the value of freshening up their image from time to time. Also our logos are designed to make you money. You have been successful in the past despite your existing logo. REALLY, your existing logo has been costing you money every time you try to use it and someone needs to trace it. Think of this as an investment."
Or something like that.