Whoever you rent it from will have his name in a plastic cover attached to the
ECV.
off topic sort of: when we were down there earlier this month (May 10th-20th) we rented an ECV for my mom. Her name is Betty, but apparently the guy at Apple
Scooter misunderstood me when we ordered it, because the name on it was Benny W.

The CM at the Safari asked her if she was sure she had the right scooter.

Yeah, she'd been driving it all week and we had called Apple Scooters the day we arrived to ask about it, to make sure bell services was giving us the right ECV.
When my husband and I took our then 3 y/o grandson down there Feb 2012, we rented a stroller from Kingdom Strollers. They asked what name we wanted on it and because our last name is so common, I asked them to put 'Levi's Buggy' on it. Before we left my D-I-L told me I was wasting my time renting a stroller for my GS as he had always refused to ride in one. I told her I wanted it just in case he decided he wanted to ride. When we picked it up and told him what the sign on it said, he got so excited and immediately jumped in. For some reason he decided Mickey Mouse sent it especially for him and we never told him any different. Anytime we came off a ride, he'd yell, "where's my buggy".

His mom couldn't believe he'd ridden in it all week, without a fight. Anyway, maybe you could have the company you rent the ECV from put something cute on the large name tag they hang on all their
ECVs.
For that matter I once had a lady here on the Dis make me a Texas license plate that had Tinkerbell and my mom's name on it. I then laminated it, punched holes in it where the screws would go, and then attached it to the back of my mom's ECV with colored zip ties. Here's a picture of it: