That old "fake diaper" trick has been around for decades, and would not stop any kind of thief. Would *you* be suspicious if you saw someone in a theme park removing a dirty diaper from a stroller? Besides, what kind of weirdo would tie a real dirty diaper onto a stroller handle when the Disney parks have trash cans every 20 feet? Soiled diapers get smelly in seconds in Florida heat; no one in his right mind would hang onto one.
Much better for deterring theft AND mistaken identity is to attach something distinctive but hard to remove; a profusion of curling ribbon, perhaps, or a lot of reflective labels. If you were a security CM and you saw someone removing such things from a stroller, it would draw your attention. Real thieves make it a point not to draw attention to themselves.
In addition to flagging your stroller in a distinctive way, the most important thing is to mark it with your name and phone number in a permanent & unobtrusive way, preferably more than once. That way, if it does wander and is found, Disney will know who it belongs to so that it can be returned. DO NOT RELY ON AN AIRLINE GATE CHECK TAG FOR ID! Those can be removed in seconds, and besides, on any given day in the parks, 30% of the strollers have an airline tag hanging on them.