Signs to watch for include whining, whimpering, howling or constant meowing; biting; constant licking of a particular body part; being unusually quiet, listless, restless or unresponsive; acting funny or out of character, either unusually aggressive or submissive; flattening ears against the head; changes in mobility, sleeping or eating patterns; or seeking more affection than usual.
A semi-colon (;) is the punctuation mark which is used to separate independent parts of a sentence or different things in a list. The sentence quoted above indicates a list of signs to watch for. You'll note that semi-colons are used to separate different groups of signs. One group is noises made by the animal ('whining, whimpering, howling or constant meowing') and another group is behavioural changes ('being unusually quiet, listless, restless or unresponsive'). So, different categories of signs are separated by semi-colons, whereas within each category, a comma is used.