We took a bunch of those colorful "Disney" Mickey shaped paint chips from Home Depot and tied those to the stroller with colorful yarn. I guess they don't have that paint anymore(or those chips), but you could use any chip and cut out Mickey shaped ones and use those.
Definitely couldn't mistake our stroller for anyone else's.
I would also re-think the umbrella strollers. We took one the first trip with my daughter and found that it really didn't have much of what we needed on it. First off, it didn't have a sun shade of any kind, so she was in the sun a lot. Next it didn't have a basket to put all of that extra kid stuff in, so it had to be carried...not fun. And there weren't any drink holders or a tray for our stuff. Lastly, it was so hot on the pavement(we went in June) that the wheels actually expanded and the rubber part just fell off the plastic rim. It was about 2 days into the trip and I had to throw it in the garbage. For the next stroller, we got this one(
http://www.toysrus.com/product/index.jsp?productId=3994452)...a Baby Trend Trendsport. It was much smaller than the travel system, but had the sun shade, tray, reclining seat, basket and was super durable. It actually became our primary stroller and lasted through 2 kids and multiple trips to WDW and everywhere else.