The obvious sign of a rat problem can be their droppings. They can produce anything up to 40 fresh droppings a day. These are tapered and usually same length of a 1p coin.  Rats are creatures of habit, and continuously use the same path when travelling. If infestation is in a garden, your see signs of worn grass and can worsen without proper treatment. They seek warm dark areas to nest. Litter can be well over 7 young and have 6 cycles a year. Locations can include loft, under floor boards, behind bath panels or even below decking in the garden.