Well, it sounds like you're asking for labels for identification and control of the right of way, rather than trying to model an actual prototype, so I'd think something pretty close to what you have been doing should be just fine.
By "customizable" I assume you mean that you just want to be able to print whatever number or code you've associated with the feature, and not a real-time changing display (like an animated billboard!). If so, an appropriate sign, in eye-catching colors and of a suitable size, can easily be printed on cardstock and trimmed to mount on a popsicle stick or equivalent (I've used coffee stirrers, dowels and balsa scale dimension lumber at various times).
It's for a different purpose, but most recently I used balsa sticks to hold up cardstock printouts of actual photographs of the prototype signage on a scratch built bridge project:
I also have used computer programs to create my own version of prototype signs, and print them out on cardstock: