Signs
for Norway Rat
You usually spot the evidence before the rat. Look for droppings near food-prep, storage, and pet-food areas, plus fresh gnaw marks, runways and burrows next to buildings and fences, and dark smudge or rub marks where rats drag their oily fur against beams and pipes. Source: https://ipm.ucanr.edu/home-and-landscape/rats/pest-notes/
Tracks in mud or dust and gnawing, climbing, or squeaking noises in walls also reveal rats. Source: https://extension.missouri.edu/publications/g9446