A few years ago, we did an article about inexpensive military toys at the dollar store.
One of the toys was some kind of storage tank, marked "Keep Clear," which I decided to turn into an objective marker.
Knowing that I wanted to keep the warning sign, I chose to touch-up the paint job, rather than priming it and making a fresh start.
I painted the pipes black, and touched up the metallic parts so that they were completely painted.
The model was then placed on a wooden base, which was then 'flocked' with coarse sand (as I intended this for use with my desert terrain). Then everything was sealed with dull clear spray, which also diminishes the 'plastic' look of the toy.
My intention is to use this for 15mm games, but it works for many scales.