I've played around with a thermal scope before and it's really interesting how it "sees" the world. If you look at a field of tall grass for example, it looks all blurry and indistinct, almost like a loose watercolour painting. Then you might spot some rocks in the field that has been lying in the sun for the whole day and those rocks would be sharply defined and very distinct because of the temperature difference.
Mammals/humans of course stand out very sharply and clearly because of the heat that warm blooded animals radiate while cold-blooded lizards/snakes are virtually invisible.
One might spot a roadsign and it would stand out very clearly because the metal's thermal qualities are completely different to the natural environment, but it's still impossible to read unless the paint itself has different thermal qualities to the metal base.
Thermal vision, is a total game changer for hunting, search & rescue and military use though. Can absolutely see why the Predators would use it, despite it's shortcomings in overall vision fidelity.