Squirrel droppings are usually going to be observed within a loft space, they are far less uniform than rat droppings and can appear in different and irregular shapes and sizes.
on the whole squirrel droppings will be round and and pellet like in appearance, theses pellets wont usually exceed 1cm in length. its also important to note that squirrel droppings will be dark brown similar to that of a rat but will turn much lighter in colour as they age.
If you are going to inspect your loft space for signs of squirrels then please remain cautious, especially if your loft space is not boarded. If in doubt of the condition of your loft space please contact a professional who can inspect the area safely.