If you actual see a rat, then you know for sure that you have a problem, and you can take proper measures of control, like buying traps to eliminate your problem. Rats are present in most cities around the globe and in most neighborhoods. Just because you do not see one, does not mean you don't have a problem. If you suspect an infestation, you need to watch out for several signs that can indicate it with certainty.
How to Tell if You Have a Rat Problem
Watch for rat droppings. Rat droppings are little pellets that most likely appear near food supplies, so check the cupboards.
Listen for scurrying noises, particularly at night.
Also the smell of a rat den (urinelike) may be a tell tale sign of a rat infestation.
Look for unexplained gnawing. Gnawing are a rodent's way of teeth care. A rat's teeth do not ever stop growing and will constantly have the need to be worn down. Look for unexplained gnawing and shavings around your home.
Watch the behavior of your pets. Are they more excited than normal? Do they constantly sniff a particular place in the wall? You may have something in the rodent family living in that particular place.
Look along walls, particularly near food. If you see a light smudge or grease smear along it, that is made by a rat. Rats memorize their environment and follow the same familiar path to and from food.